DISPATCH Working Group J.J. Garcia Aranda
J. Perez Lajo
Internet Draft L.M. Diaz Vizcaino
G. Munoz Fernandez
Intended status: Standards Track Alcatel-Lucent
Expires: January 2018 C. Barcenilla
M. Cortes
J. Salvachua
J. Quemada
Univ. Politecnica de Madrid
M. Narganes Quijano
Tecnalia
I. Martinez Sarriegui
L. Fajardo Ibanez
P. Lopez Zapico
Optiva
July 18, 2017
The Quality for Service Protocol
draft-aranda-dispatch-q4s-04.txt
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on January 18, 2018.
Garcia Aranda Expires January 18, 2018 [Page 1]
Internet-Draft The Quality for Services Protocol July 2017
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document.
Abstract
This memo describes an application level protocol for the standard
communication of e2e QoS compliance information using a protocol
based on Hypertext Transfer Protocol (HTTP), which forms the basis
for the World Wide Web, and Session Description Protocol (SDP).
Quality for Service Protocol (Q4S) provides a mechanism for latency,
jitter, bandwidth and packet loss negotiation and monitoring,
alerting whenever one of the negotiated conditions is violated.
Implementation details on the actions to be triggered upon
reception/detection of QoS alerts exchanged by the protocol are out
of scope of this draft, it is application dependent (e.g. increase
quality, reduce bit-rate) or even network dependent (e.g. change
connection's quality profile).
Table of Contents
1. Introduction...................................................5
1.1. Motivation................................................6
1.2. Summary of Features.......................................7
2. Terminology....................................................8
3. Overview of Operation..........................................8
4. Q4S messages..................................................20
4.1. Requests.................................................20
4.2. Responses................................................21
4.3. Header Fields............................................23
4.3.1. Common Q4S Header Fields............................23
4.3.2. Specific Q4S Request Header Fields..................23
4.3.3. Specific Q4S Response Header Fields.................25
4.4. Bodies...................................................25
4.4.1. Encoding............................................25
Garcia Aranda Expires January 18, 2018 [Page 2]
Internet-Draft The Quality for Services Protocol July 2017
5. Q4S method definitions........................................26
5.1. BEGIN....................................................26
5.2. READY....................................................26
5.3. PING.....................................................27
5.4. BWIDTH...................................................27
5.5. Q4S-ALERT................................................27
5.6. Q4S-RECOVERY.............................................28
5.7. CANCEL...................................................29
6. Response codes................................................29
6.1. 100 Trying...............................................29
6.2. Success 2xx..............................................29
6.2.1. 200 OK..............................................29
6.3. Redirection 3xx..........................................30
6.4. Request Failure 4xx......................................30
6.4.1. 400 Bad Request.....................................30
6.4.2. 404 Not Found.......................................30
6.4.3. 405 Method Not Allowed..............................30
6.4.4. 406 Not Acceptable..................................30
6.4.5. 408 Request Timeout.................................31
6.4.6. 413 Request Entity Too Large........................31
6.4.7. 414 Request-URI Too Long............................31
6.4.8. 415 Unsupported Media Type..........................31
6.4.9. 416 Unsupported URI Scheme..........................31
6.5. Server Failure 5xx.......................................31
6.5.1. 500 Server Internal Error...........................31
6.5.2. 501 Not Implemented.................................31
6.5.3. 503 Service Unavailable.............................32
6.5.4. 504 Server Time-out.................................32
6.5.5. 505 Version Not Supported...........................32
6.5.6. 513 Message Too Large...............................32
6.6. Global Failures 6xx......................................32
6.6.1. 600 session does not exist..........................33
6.6.2. 601 quality level not allowed.......................33
6.6.3. 603 Session not allowed.............................33
6.6.4. 604 authorization not allowed.......................33
7. Protocol......................................................33
7.1. Protocol Phases..........................................33
7.2. SDP Structure............................................35
7.2.1. "qos-level" attribute...............................36
7.2.2. "alerting-mode" attribute...........................37
7.2.3. "alert-pause" attribute.............................37
7.2.4. "recovery-pause" attribute..........................37
7.2.5. "public-address" attributes.........................38
7.2.6. "latency" attribute.................................38
7.2.7. "jitter" attribute..................................38
7.2.8. "bandwidth" attribute...............................38
7.2.9. "packetloss" attribute..............................38
Garcia Aranda Expires January 18, 2018 [Page 3]
Internet-Draft The Quality for Services Protocol July 2017
7.2.10. "flow" attributes..................................39
7.2.11. Measurement attributes.............................40
7.3. Measurements.............................................41
7.3.1. Latency.............................................42
7.3.2. Jitter..............................................42
7.3.3. Bandwidth...........................................43
7.3.4. Packet loss.........................................45
7.4. Handshake Phase..........................................46
7.5. Negotiation phase........................................47
7.5.1. Stage 0: Measurement of latencies and jitters.......49
7.5.2. Stage 1: Measurement of bandwidth and packet loss...52
7.5.3. Quality constraints not reached.....................55
7.5.3.1. Actuator role..................................58
7.5.3.2. Policy server role.............................59
7.5.4. QoS Level changes...................................59
7.6. Continuity phase.........................................60
7.7. Termination Phase........................................63
7.8. Dynamic constraints and flows............................64
7.9. Qos-level upgrade and downgrade operation................65
8. General User Agent behavior...................................67
8.1. Roles in peer to peer scenarios..........................67
8.2. Multiple Quality sessions in parallel....................68
8.3. General client behavior..................................69
8.3.1. Generating requests.................................70
8.4. General server behavior..................................70
9. Implementation Recommendations................................71
9.1. Default client constraints...............................71
9.2. Latency and Jitter measurements..........................71
9.3. Bandwidth measurements...................................72
9.4. Packet loss measurement resolution.......................72
9.5. Measurements and reactions...............................73
9.6. Instability treatments...................................73
9.7. Scenarios................................................74
9.7.1. Client to ACP.......................................74
9.7.2. Client to client....................................75
10. Security Considerations......................................75
11. IANA Considerations..........................................75
12. Conclusions..................................................79
13. References...................................................80
13.1. Normative References....................................80
13.2. Informative References..................................81
14. Acknowledgments..............................................82
15. Authors' Addresses...........................................83
Garcia Aranda Expires January 18, 2018 [Page 4]
Internet-Draft The Quality for Services Protocol July 2017
1. Introduction
The World Wide Web (WWW) is a distributed hypermedia system which
has gained widespread acceptance among Internet users. Although WWW
browsers support other, preexisting Internet application protocols,
the native and primary protocol used between WWW clients and servers
is the HyperText Transfer Protocol (HTTP) (RFC 2616 [1]). The ease
of use of the Web has prompted its widespread employment as a
client/server architecture for many applications. Many of such
applications require the client and the server to be able to
communicate each other and exchange information with certain quality
constraints.
Quality in communications at application level consists of four
measurable parameters:
o Latency: The time a message takes to travel from source to
destination. It may be approximated to RTT/2 (Round trip time),
assuming the networks are symmetrical. In this context we will
consider the statistical median formula.
o Jitter: latency variation. There are some formulas to calculate
Jitter, and in this context we will consider the arithmetic
mean formula.
o Bandwidth: bit rate of communication. To assure quality, a
protocol MUST assure the availability of the bandwidth needed
by the application.
o Packet loss: The percentage of packet loss is closely related
to bandwidth and jitter. Affects bandwidth because a high
packet loss implies sometimes retransmissions that also
consumes extra bandwidth, other times the retransmissions are
not achieved (for example in video streaming over UDP) and the
information received is less than the required bandwidth. In
terms of jitter, a packet loss sometimes is seen by the
destination like a larger time between arrivals, causing a
jitter growth.
Any other communication parameter such as throughput is not a
network parameter because depends on protocol window size and other
implementation-dependent aspects.
Q4S provides a mechanism for quality monitoring based on an HTTP
syntax and SDP in order to be easily integrated in WWW, but it may
be used by any type of application, not only those based on HTTP.
Quality requirements may be needed by any type of application that
Garcia Aranda Expires January 18, 2018 [Page 5]
Internet-Draft The Quality for Services Protocol July 2017
communicates using any kind of protocol, especially those with real-
time constraints. Depending on the nature of each application the
constraints may be different leading to different parameter
thresholds that need to be met.
Q4S is an application level Client/Server protocol that continuously
measures session quality for a given flow (or set of flows), end-to-
end and in real-time; raising alerts if quality parameters are below
a given pre-negotiated threshold and sending recoveries when quality
parameters are restored. Q4S describes when these notifications,
alerts and recoveries, need to be sent and the entity receiving
them. The actions undertaken by the receiver of the alert are out of
scope of the protocol.
Q4S is session-independent from the application flows, to minimize
the impact on them. To perform the measurements, two control flows
are created on both communication paths (forward and reverse
directions).
1.1. Motivation
Monitoring quality of service (QoS) in computer networks is useful
for several reasons:
o Enable real-time services and applications to verify whether
network resources achieve a certain QoS level. This helps real-
time services and applications to run through the Internet,
allowing the existence of Application Content providers (ACPs)
which offer guaranteed real-time services to the final users.
o Real-time monitoring allows applications to adapt themselves to
network conditions (Application-based QoS) and/or request more
network quality to the ISP (if the ISP offers this
possibility).
o Monitoring may also be required by Peer to Peer (P2P) real-time
applications for which Q4S can be used
o Enable ISPs to offer QoS to any ACP or final user application
in an accountable way
o Enable e2e negotiation of QoS parameters, independently of the
Internet service providers of both endpoints.
A protocol to monitor QoS must address the following issues:
Garcia Aranda Expires January 18, 2018 [Page 6]
Internet-Draft The Quality for Services Protocol July 2017
o Must be ready to be used in conjunction with current standard
protocols and applications, without forcing a change on them.
o Must have a formal and compact way to specify quality
constraints of the desired application to run.
o Must have measurement mechanisms avoiding application
disruption, minimizing network resources consumption.
o Must have specific messages to alert about the violation of
quality constraints in different directions (forward and
reverse), because network routing may not be symmetrical, and
of course, quality constraints may not be symmetrical.
o After having alerted about the violation of quality
constraints, must have specific messages to inform about
recovery of quality constraints in corresponding directions
(forward and reverse).
o Must protect the data (constrains, measurements, QoS levels
demanded from the network) in order to avoid the injection of
malicious data in the measurements.
1.2. Summary of Features
Quality for Service (Q4S) is a message-oriented communication
protocol that can be used in conjunction with any other application-
level protocol. Q4S protocol is a measurement protocol. Any taken
action derived from its measurements are out of scope of the
protocol. These actions depend on application provider and may be
application-level adaptive reactions, may involve requests to ISP,
or whatever application provider decide.
The benefits in quality measurements provided by Q4S can be used by
any type of application that uses any type of protocol for data
transport. It provides a quality monitoring scheme for any
communication that takes place between the client and the server,
not only for the Q4S communication itself.
Q4S does not establish multimedia sessions and it does not transport
application data. It monitors the fulfillment of the quality
requirements of the communication between the client and the server,
and therefore does not impose any restrictions on the type of
application, protocol or the type of usage of the monitored quality
connection.
Garcia Aranda Expires January 18, 2018 [Page 7]
Internet-Draft The Quality for Services Protocol July 2017
Some applications may vary their quality requirements dynamically
for any given quality parameter. Q4S is able to adapt to the
changing application needs modifying the parameter thresholds to the
new values and monitoring the network quality according to the new
quality constraints. It will raise alerts if the new constraints are
violated.
Q4S session lifetime is composed of four phases with different
purposes: Handshake, Negotiation, Continuity and Termination.
Negotiation and Continuity phases perform network parameter
measurements as per a negotiated measurement procedure. Different
measurement procedures COULD be used inside Q4S, although one
default measurement mechanism is needed for compatibility reasons
and is the one defined in this draft. Basically, Q4S defines how to
transport application quality requirements and measurement results
between client and server and providing monitoring and alerting too.
Q4S MUST be executed just before starting a client-server
application which needs a quality connection in terms of latency,
jitter, bandwidth and/or packet loss. Once client and server have
succeeded in establishing communication under quality constraints,
the application can start, and Q4S continues measuring and alerting
if necessary.
The quality parameters can be suggested by the client in the first
message of the handshake phase, but it's the server that accepts
these parameter values or forces others. The server is in charge of
deciding the final values of quality connection.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119 [3].
3. Overview of Operation
This section introduces the basic operation of Q4S using simple
examples. This section is of tutorial nature and does not contain
any normative statements.
The first example shows the basic functions of a Q4S: communication
establishment between a client and a server, quality requirement
negotiations for the requested application, application start and
Garcia Aranda Expires January 18, 2018 [Page 8]
Internet-Draft The Quality for Services Protocol July 2017
continuous quality parameter measurements, and finally communication
termination.
The client triggers the establishment of the communication
requesting a specific service or application from the server. This
first message must have a special URI (RFC 3986), which may force
the use of the Q4S protocol if it is implemented in a standard web
browser. This message consists of a Q4S BEGIN method, which can
optionally include a proposal for the communication quality
requirements in an SDP body. This option gives the client a certain
negotiation capacity about quality requirements, but it will be the
server who finally decides about the stated requirements.
This request is answered by the server with a Q4S 200 OK response
letting the client know that it accepts the request. This response
message MUST contain an SDP body with:
o The assigned Q4S session id.
o The quality constraints required by the requested application.
o The measurement procedure to use.
o The alerting mode: there are two different scenarios for
sending alerts that trigger actions either on the network or in
the application when measurements identify violated quality
constraints. In both cases, alerts are triggered by the server.
o a) Q4S-aware-network scenario: the network is Q4S aware,
and reacts by itself to these alerts. In this scenario Q4S
ALERT messages are sent by the server to the client, and
network elements inspect and process these alert message.
The alerting mode in this scenario is called Q4S-aware-
network alerting mode.
o b) Reactive scenario: the network is not Q4S aware. In this
scenario alert notifications are sent to a specific node,
called Actuator, which is in charge of taking decisions
regarding what actions to trigger: either to change
application behavior to adapt it to network conditions
and/or invoke a network policy server in order to
reconfigure the network and request more quality for
application flows.
Garcia Aranda Expires January 18, 2018 [Page 9]
Internet-Draft The Quality for Services Protocol July 2017
+------+ +-----------+
| App ||Application|
|Client| +-----------+
+------+ A
|
+------+ +------+ +--------+
| Q4S || Q4S ||Actuator|
|Client| |Server| +--------+
+------+ +------+ |
V
+-------------+
|policy server|
+-------------+
Figure 1 Reactive scenario
o The format of messages exchanged between the server stack and
the Actuator, doesn't follow Q4S codification rules, but their
format will be implementation dependent. In this way, we will
call "notifications" to the messages sent from the server stack
to the Actuator (e.g. alert notifications), and "acknowledges"
to messages sent from the Actuator to the server stack in
response to notifications (e.g. alert acknowledges).alert-
pause: the amount of time between consecutive alerts. In the
Q4S-aware-network scenario, the server has to wait this period
of time between Q4S ALERT messages sent to the client. In the
Reactive scenario, the server stack has to wait this period of
time between alert notifications sent to the Actuator.
Measurements are not stopped in Negotiation or Continuity
Phases during this period of time, but no alerts are fired even
with violated network quality constraints in order to leave
time for network reconfiguration or for application adjustments
o recovery-pause: The amount of time the Q4S server waits before
trying to recover initial qos-level. After having detected
violation of quality constraints several times, the qos-level
will have been increased accordingly. If this violation
detection finally stops, the server waits for a period of time
(recovery time) and if the situation persists, it tries to
recover to previous qos-level values gradually by sending Q4S
RECOVERY messages to the client, in the Q4S-aware-network
scenario, or recovery notifications to the Actuator, in the
Reactive scenario.
Garcia Aranda Expires January 18, 2018 [Page 10]
Internet-Draft The Quality for Services Protocol July 2017
It is important to highlight that any Q4S 200 OK response sent by
the server to the client at any time during the life of a quality
session may contain an SDP body with new values of quality
constraints required by the application. Depending on the phase and
the state of the measurement procedure within the specific phase,
the client will react accordingly so as to take into account the new
quality constraints in the measurement procedure.
Once the communication has been established (handshake phase is
finished), the protocol will verify that the communication path
between the client and the server meets the quality constraints on
both directions, from and to the server (negotiation phase). This
negotiation phase requires taking measurements of the quality
parameters: latencies, jitter, bandwidth and packet loss. This phase
is initiated with a client message containing a Q4S READY method,
which will be answered by the server with a Q4S 200 OK response.
Negotiation measurements are achieved in two sequential stages:
o Stage 0: latency and jitter measurements
o Stage 1: bandwidth and packet loss measurements
Stage 0 measurements are being taken through Q4S PING messages sent
both from both the client and the server. All Q4S PING requests will
be answered by Q4S 200 OK messages to allow for bidirectional
measurements.
After a pre-agreed number of measurements have been performed,
determined by the measurement procedure sent by the server, three
scenarios may be possible:
a) Measurements do not meet the requirements: in this case the stage
0 is repeated after sending an alert from the server to the
client or from the server stack to the Actuator, depending on the
alerting mode defined in the Handshake phase. Notice that
measurements continue to be taken but no alerts are fired during
the alert-pause time. In the Reactive scenario, the Actuator will
decide either to forward the alert notification to the network
policy server or to the application, depending on where
reconfiguration actions have to be taken.
b) Measurements do meet the requirements: in this case client moves
to stage 1 sending a new READY message.
c) At any time during the measurement procedure, the Q4S 200 OK
message sent by the server to the client, in response to a Q4S
Garcia Aranda Expires January 18, 2018 [Page 11]
Internet-Draft The Quality for Services Protocol July 2017
PING message, contains an SDP body with new values of quality
constraints required by the application; this means the
application has varied their quality requirements dynamically and
therefore quality thresholds used while monitoring quality
parameters have to be changed to the new constraints. In this
case the client moves to the beginning of the Stage 0 for
initiating the negotiation measurements again.
Stage 1 is optional. Its purpose is to measure the availability of
application needed bandwidth. This stage can be skipped by client
sending a "READY 2" message after completion of stage 0 when
bandwidth requirements is set to cero kbps in the SDP. Stage 1
measurements are achieved through Q4S BWIDTH messages sent both from
the client and the server. Unlike PING messages, Q4S BWIDTH requests
will not be answered.
If Stage 0 and 1 meet the application quality constraints, the
application may start. Q4S will enter the continuity phase measuring
the network quality parameters through the Q4S PING message exchange
on both connection paths, and raising alerts in case of violation. .
Once the client wants to terminate the quality session it sends a
Q4S CANCEL message, which will be acknowledged by the server with
another Q4S CANCEL message. Termination of quality sessions are
always initiated by the client because Q4S TCP requests follow the
client server schema.
This figure depicts the message exchange in a successful scenario.
Garcia Aranda Expires January 18, 2018 [Page 12]
Internet-Draft The Quality for Services Protocol July 2017
+-------------------------------------------+
| |
| Client Server |
| |
Handshake | --------- Q4S BEGIN -----------> |
| |
| |
| |
| --------- Q4S PING ------------> |
| |
| |
| |
| |
| |
| |
| |
| |
Termination | --------- Q4S CANCEL ----------> | app end
|
Internet-Draft The Quality for Services Protocol July 2017
Client and server measurements are included into PING and BWIDTH
messages, allowing both sides of the communication to be are aware
of all measurements in both directions.
The following two examples show the behavior of the Q4S protocol
when: quality constraints are violated, alerts are generated; and,
later on, violation of quality constraints stops leadig to the
execution of the recovery process. The first example shows the Q4S-
aware-network alerting mode scenario:
Garcia Aranda Expires January 18, 2018 [Page 14]
Internet-Draft The Quality for Services Protocol July 2017
+-------------------------------------------+
| |
| Client Server |
| |
Handshake | --------- Q4S BEGIN -----------> |
| |
| |
| |
| ... |
| |
| |
| (alert-pause start) |
Repetition | |
of Stage 0 | --------- Q4S READY 0----------> |
| |
| |
| |
| |
| |
| |
| ... |
|(alert-pause expires & |
| violated constraints) |
|
Internet-Draft The Quality for Services Protocol July 2017
| --------- Q4S ALERT -----------> |
| |
| (alert-pause start) |
| --------- Q4S PING ------------> |
| |
| ... |
|(alert-pause expires & |
| violated constraints) |
| |
| (alert-pause) |
| --------- Q4S PING ------------> |
| |
| ... |
|(alert-pause expires & |
| Fullfilled constraints) |
| |
| (recovery-pause start) |
| |
| --------- Q4S PING ------------> |
| |
| ... |
|(recovery-pause expires & |
| Fullfilled constraints) |
| --------- Q4S RECOVERY ---------> |
| |
| |
| ... |
| |
Termination | --------- Q4S CANCEL ----------> | app end
|
Internet-Draft The Quality for Services Protocol July 2017
In this Q4S-aware-network alerting mode scenario, the server may
send Q4S alerts to the client at any time on detection of violated
quality constraints. This alerting exchange must not interrupt the
continuity quality parameter measurements between client and server.
The second example depicted in the following figure represents the
Reactive scenario, in which alert notifications are sent from the
server stack to the Actuator who is in charge of deciding either to
act over application behavior and/or invoke a network policy server.
The Actuator is an entity that has a pre-defined set of different
quality levels and decides how to act depending on the actions
stated for each of these levels; it can take actions for making
adjustments on the application or it can send a request to the
policy server for acting on the network. The policy server also has
a pre-defined set of different quality levels pre-agreed upon
between the Application Content Provider and the ISP. The Reactive
alerting mode is the default mode.
Garcia Aranda Expires January 18, 2018 [Page 17]
Internet-Draft The Quality for Services Protocol July 2017
+-------------------------------------------+
| |
| Client Server Actuator |
Handshake | ----- Q4S BEGIN -----> |
| |
| |
| |
| ... |
| (alert-pause start) |
| --alert |
| notification--> |
| |
| |
| |
| |
| |
| |
| |
|
Internet-Draft The Quality for Services Protocol July 2017
| |
| ----- Q4S BWITDH ----> |
| |
| |
| |
| |
|(recovery-pause expires & |
| fulfilled constraints) |
| |
| --alert |
| notification--> |
| |
| |
| ----- Q4S PING ------> |
| ... |
| |
Termination | ----- Q4S CANCEL ----> | app end
| --cancel |
| notification--> |
| |
|
Internet-Draft The Quality for Services Protocol July 2017
interrupted. This way, both the client and the server will detect
network improvements as soon as possible. In a similar way, during
the continuity phase, the server may send alert notifications at any
time to the Actuator on detection of violated quality constraints.
This alerting exchange must not interrupt the continuity
measurements between client and server.
Finally, in the Termination phase, Q4S CANCEL messages sent from the
client to the server must be forwarded from the server to the
Actuator in order to release possible assigned resources for the
session.
4. Q4S messages
Q4S is a text-based protocol and uses the UTF-8 charset (RFC 3629
[11]). A Q4S message is either a request or a response.
Both Request and Response messages use the basic format of Internet
Message Format (RFC 5322 [12]). Both types of messages consist of a
start-line, one or more header fields, an empty line indicating the
end of the header fields, and an optional message-body.
generic-message = start-line
*message-header
CRLF
[ message-body ]
start-line = Request-Line / Status-Line
The start-line, each message-header line, and the empty line MUST be
terminated by a carriage-return line-feed sequence (CRLF). Note
that the empty line MUST be present even if the message-body is not.
Much of Q4S's messages and header field syntax are identical to
HTTP/1.1. However, Q4S is not an extension of HTTP.
4.1. Requests
Q4S requests are distinguished by having a Request-Line for a start-
line. A Request-Line contains a method name, a Request-URI, and the
protocol version separated by a single space (SP) character.
Garcia Aranda Expires January 18, 2018 [Page 20]
Internet-Draft The Quality for Services Protocol July 2017
The Request-Line ends with CRLF. No CR or LF are allowed except in
the end-of-line CRLF sequence. No linear whitespace (LWS) is allowed
in any of the elements.
Request-Line = Method SP Request-URI SP Q4S-Version CRLF
Method: This specification defines seven methods: BEGIN for starting
and negotiate quality sessions, READY for synchronization of
measurements, PING and BWIDTH for quality measurements
purpose, CANCEL for terminating sessions, Q4S-ALERT for
quality violations reporting, and Q4S-RECOVERY for quality
recovery reporting.
Request-URI: The Request-URI is a Q4S URI (RFC 2396) as described in
7.4. The Request-URI MUST NOT contain unescaped spaces or
control characters and MUST NOT be enclosed in "<>".
Q4S-Version: Both request and response messages include the version
of Q4S in use. To be compliant with this specification,
applications sending Q4S messages MUST include a Q4S-Version
of "Q4S/1.0". The Q4S-Version string is case-insensitive,
but implementations MUST send upper-case. Unlike HTTP/1.1,
Q4S treats the version number as a literal string. In
practice, this should make no difference.
4.2. Responses
Q4S responses are distinguished from requests by having a Status-
Line as their start-line. A Status-Line consists of the protocol
version followed by a numeric Status-Code and its associated textual
phrase, with each element separated by a single SP character. No CR
or LF is allowed except in the final CRLF sequence.
Status-Line = Q4S-Version SP Status-Code SP Reason-Phrase CRLF
The Status-Code is a 3-digit integer result code that indicates the
outcome of an attempt to understand and satisfy a request. The
Reason-Phrase is intended to give a short textual description of the
Status-Code. The Status-Code is intended for use by automata,
whereas the Reason-Phrase is intended for the human user. A client
is not required to examine or display the Reason-Phrase.
While this specification suggests specific wording for the reason
phrase, implementations MAY choose other text, for example, in the
Garcia Aranda Expires January 18, 2018 [Page 21]
Internet-Draft The Quality for Services Protocol July 2017
language indicated in the Accept-Language header field of the
request.
The first digit of the Status-Code defines the class of response.
The last two digits do not have any categorization role. For this
reason, any response with a status code between 100 and 199 is
referred to as a "1xx response", any response with a status code
between 200 and 299 as a "2xx response", and so on. Q4S/1.0 allows
following values for the first digit:
1xx: Provisional -- request received, continuing to process
the request;
2xx: Success -- the action was successfully received,
understood, and accepted;
3xx: Redirection -- further action needs to be taken in order
to complete the request;
4xx: Request Failure -- the request contains bad syntax or
cannot be fulfilled at this server;
5xx: Server Error -- the server failed to fulfill an
apparently valid request;
6xx: Global Failure -- the request cannot be fulfilled at any
server.
The status codes are the same described in HTTP (RFC 2616 [1]). In
the same way as HTTP, Q4S applications are not required to
understand the meaning of all registered status codes, though such
understanding is obviously desirable. However, applications MUST
understand the class of any status code, as indicated by the first
digit, and treat any unrecognized response as being equivalent to
the x00 status code of that class.
The Q4S-ALERT, Q4S-RECOVERY and CANCEL requests do not have to be
responded. However, after receiving a Q4S-ALERT, Q4S-RECOVERY or
CANCEL request, the server SHOULD sends a Q4S-ALERT, Q4S-RECOVERY or
CANCEL request to the client
Garcia Aranda Expires January 18, 2018 [Page 22]
Internet-Draft The Quality for Services Protocol July 2017
4.3. Header Fields
Q4S header fields are identical to HTTP header fields in both syntax
and semantics.
Some header fields only make sense in requests or responses. These
are called request header fields and response header fields,
respectively. If a header field appears in a message not matching
its category (such as a request header field in a response), it MUST
be ignored.
4.3.1. Common Q4S Header Fields
These fields may appear in Request and Response messages.
o Session-Id: the value for this header is the same session id
used in SDP (embedded in "o" SDP parameter) and is assigned by
the server. The messages without SDP MUST include this header.
If a message has and SDP body, this header is optional. The
method of allocation is up to the creating tool,
but it is suggested that a UTC timestamp be used to ensure
uniqueness.
o Sequence-Number: sequential and cyclic positive integer number
assigned to PING and BWIDTH messages, and acknowledged in 200
OK responses.
o Timestamp: this optional header contains the system time (with
the best possible accuracy). It indicates the time in which the
PING request was sent. If this header is present in PING
messages, then the 200 OK response messages include this value.
o Stage: this is used in client's READY requests and server's
200 OK responses during the Negotiation and Continuity phases
in order to synchronize the initiation of the measurements.
Example: Stage: 0
4.3.2. Specific Q4S Request Header Fields
In addition to HTTP header fields, these are the specific Q4S
request header fields
Garcia Aranda Expires January 18, 2018 [Page 23]
Internet-Draft The Quality for Services Protocol July 2017
o User-Agent: this header contains information about the
implementation of the user agent. This is for statistical
purposes, the tracing of protocol violations, and the automated
recognition of user agents for the sake of tailoring responses
to avoid particular user agent limitations. User agents SHOULD
include this field with requests. The field can contain
multiple product tokens and comments identifying the agent and
any sub-products which form a significant part of the user
agent. By convention, the product tokens are listed in order of
their significance for identifying the application.
o Signature: this header contains a digital signature that can be
used by the network or policy server to validate the SDP,
preventing security attacks. The signature is an optional
header generated by the server according to the pre-agreed
security policies between the Application Content Provider and
the ISP. For example, a hash algorithm and encryption method
such as MD5 (RFC 1321 [6]) and RSA (RFC 2437 [7]) based on the
server certificate could be used. This certificate is supposed
to be delivered by a Certification Authority (CA) or policy
owner to the server. The signature is applied to the SDP body.
Signature= RSA ( MD5 (), )
If the signature is not present, other validation mechanism may
be implemented in order to provide assured quality with
security and control.
o Measurements: this header carries the measurements of the
quality parameters in PING and BWIDTH requests. The format is:
Measurements: "l=" " "|[0..9999] ", j=" " "|[0..9999] ", pl=" "
"|[0.00 .. 100.00] ", bw=" " "|[0..9999]
Where "l" stands for latency followed by the measured value or
an empty space, "j" stands for jitter followed by the measured
value or an empty space, "pl" stands for packetloss followed by
the measured value in % or an empty space and "bw" stands for
bandwidth followed by the measured value or an empty space.
Garcia Aranda Expires January 18, 2018 [Page 24]
Internet-Draft The Quality for Services Protocol July 2017
4.3.3. Specific Q4S Response Header Fields
o Expires: its purpose is to provide a sanity check and allow the
server to close inactive sessions. If the client does not send
a new request before the expiration time, the server MAY close
the session. The value MUST be an integer and the measurement
units are milliseconds.
In order to keep the session open the server MUST send a Q4S
alert before the session expiration (Expires header), with the
same quality levels and an alert cause of "keep-alive". The
purpose of this alert is to avoid TCP sockets (which were
opened with READY message) from being closed, specially in NAT
scenarios.
4.4. Bodies
Requests, including new requests defined in extensions to this
specification, MAY contain message bodies unless otherwise noted.
The interpretation of the body depends on the request method.
For response messages, the request method and the response status
code determine the type and interpretation of any message body. All
responses MAY include a body.
The Internet media type of the message body MUST be given by the
Content-Type header field.
4.4.1. Encoding
The body MUST NOT be compressed. This mechanism is valid for
other protocols such as HTTP and SIP (RFC 3261 [13]), but
a compression/coding scheme will limit certain logical
implementations of the way the request is parsed, thus, making the
protocol concept more implementation dependent. In addition,
bandwidth calculation may not be valid if compression is used.
Therefore, the HTTP request header "Accept-Encoding" cannot be used
in Q4S with different values than "identity" and if it is present in
a request, the server MUST ignore it. In addition, the response
header "Content-Encoding" is optional, but if present, the unique
permitted value is "identity".
The body length in bytes is provided by the Content-Length header
field. The "chunked" transfer encoding of HTTP/1.1 MUST NOT be used
for Q4S (Note: The chunked encoding modifies the body of a message
Garcia Aranda Expires January 18, 2018 [Page 25]
Internet-Draft The Quality for Services Protocol July 2017
in order to transfer it as a series of chunks, each one with its own
size indicator.)
5. Q4S method definitions
The Method token indicates the method to be performed on the
resource identified by the Request-URI. The method is case-
sensitive.
Method = "BEGIN" | "READY" | "PING" | "BWIDTH" |
"Q4S-ALERT" | "Q4S-RECOVERY" | "CANCEL" |
extension-method
extension-method = token
The list of methods allowed by a resource can be specified in an
"Allow" header field (RFC 2616 [1] section 14.7). The return code of
the response always notifies the client when a method is currently
allowed on a resource, since the set of allowed methods can change
dynamically. Any server application SHOULD return the status code
405 (Method Not Allowed) if the method is known, but not allowed for
the requested resource, and 501 (Not Implemented) if the method is
unrecognized or not implemented by the server.
5.1. BEGIN
The BEGIN method requests information from a resource identified by
a Q4S URI. The semantics of this method is the starting of a quality
session.
This method is only used during the handshake phase to retrieve the
SDP containing session id and all quality and operation parameters
for the desired application to run.
When a BEGIN message is received by the server, any current quality
session is cancelled and a new session should be created.
The response to a Q4S BEGIN request is not cacheable.
5.2. READY
The READY method is used to synchronize the starting time for
sending of PING and BWIDTH messages over UDP between clients and
servers. The stage header included in this method is mandatory.
Garcia Aranda Expires January 18, 2018 [Page 26]
Internet-Draft The Quality for Services Protocol July 2017
This message is only used in negotiation and continuity phases, and
only just before making a measurement. Otherwise (out of this
context), the server MUST ignore this method.
5.3. PING
This message is used during the negotiation and continuity phases to
measure the RTT and jitter of a session. The message MUST be sent
only over UDP ports.
The fundamental difference between the PING and BWIDTH requests is
reflected in the different measurements achieved with them. PING is
a short message, and MUST be answered in order to measure RTT and
jitter, whereas BWIDTH is a long message (1 Kbyte or more) and MUST
NOT be answered.
PING is a request method that can be originated by client but also
by server. Client MUST also answer the server PING messages,
assuming a "server role" for these messages during measurement
process.
The Measurements header included in this method is mandatory, and
provides updated measurements values for latency, jitter and packet
loss to the counterpart.
5.4. BWIDTH
This message is used only during the Negotiation phase to measure
the bandwidth and packet loss of a session. The message MUST be sent
only over UDP ports.
BWIDTH is a request method that can be originated by the client but
also by server. Both (client and server) MUST NOT answer BWIDTH
messages.
The Measurements header included in this method is mandatory, and
provides updated measurements values for bandwidth and packet loss
to the counterpart.
5.5. Q4S-ALERT
This is the request message that Q4S generates when the measurements
indicate that quality constraints are being violated. It is used
during the negotiation and continuity phases.
Garcia Aranda Expires January 18, 2018 [Page 27]
Internet-Draft The Quality for Services Protocol July 2017
This informative message indicates that the user experience is being
degraded and includes the details of the problem (bandwidth, jitter,
packet loss measurements). The Q4S-ALERT message does not contain
any detail on the actions to be taken, which depends on the
agreements between all involved parties.
Q4S-ALERT request does not have to be answered with a response
message unless there is an error condition. However, after receiving
a Q4S-ALERT request, the counterpart answers with a Q4S-ALERT
request. The response to a Q4S-ALERT request is not cacheable.
This method is always initiated by the server in both alerting
modes. In Q4S-aware-network alerting mode, the Q4S-ALERT messages
are fired by the server and sent to the client, advising the network
to react by itself. In Reactive alerting mode. alert notifications
are triggered by the server stack and sent to the Actuator.(see
Figure1 "Reactive Scenario")
Client----q4s----SERVER STACK--->ACTUATOR-->APP OR POLICY SERVER
The way in which the server stack notifies the Actuator is
implementation dependent, and the communication between the Actuator
and the network policy server is defined by the protocol and API
that the policy server implements.
5.6. Q4S-RECOVERY
This is the request message that Q4S generates when the measurements
indicate that quality constraints were being violated but they have
been fulfilled during a period of time already (recovery pause). It
is used during the negotiation and continuity phases.
This informative message indicates that the qos-level could be
increased gradually until the initial qos-level is recovered (the
qos-level established at the beginning os the session of that was
decreased during violation of constraints). The Q4S-RECOVERY message
does not contain any detail on the actions to be taken, which
depends on the agreements between all involved parties.
Q4S- RECOVERY request does not have to be answered with a response
message unless there is an error condition. However, after receiving
a Q4S- RECOVERY request, the counterpart answers with a Q4S-
RECOVERY request. The response to a Q4S- RECOVERY request is not
cacheable.
As for the Q4S-ALERT message, the Q4S-RECOVERY method is always
initiated by the server in both alerting modes. In Q4S-aware-network
Garcia Aranda Expires January 18, 2018 [Page 28]
Internet-Draft The Quality for Services Protocol July 2017
alerting mode, the Q4S-RECOVERY messages are fired by the server and
sent to the client, advising the network to react by itself. In
Reactive alerting mode, recovery notifications are triggered by the
server stack and sent to the Actuator.(see Figure1 "Reactive
Scenario")
5.7. CANCEL
The semantics of CANCEL message is the release of the Q4S session id
and the possible resources assigned to the session. This message
could be triggered by Q4S stack or by the application using the
stack (through an implementation dependent API).
In the same way as Q4S-ALERT, CANCEL must not be answered with a
response message. However, if the server receives a CANCEL message,
it must answer with a CANCEL request message towards the client,
acknowledging the reception.
In the Reactive scenario, the server stack MUST react to the Q4S
CANCEL messages received from the client by forwarding a cancel
notification to the Actuator, in order to release possible assigned
resources for the session (at application or at policy server). The
Actuator must answer the cancel notification with a cancel
acknowledge towards the server stack, acknowledging the reception.
6. Response codes
Q4S response codes are used for TCP and UDP. However, in UDP only
the response code 200 is used.
6.1. 100 Trying
This response indicates that the request has been received by the
next-hop server and that some unspecified action is being taken on
behalf of this request (for example, a database is being consulted).
This response, like all other provisional responses, stops
retransmissions of a Q4S-ALERT during the alert-pause time.
6.2. Success 2xx
2xx responses give information about success of a request.
6.2.1. 200 OK
The request has succeeded.
Garcia Aranda Expires January 18, 2018 [Page 29]
Internet-Draft The Quality for Services Protocol July 2017
6.3. Redirection 3xx
3xx responses give information about the user's new location, or
about alternative services that might be able to satisfy the
request.
The requesting client SHOULD retry the request at the new
address(es) given by the Location header field.
6.4. Request Failure 4xx
4xx responses are definite failure responses from a particular
server. The client SHOULD NOT retry the same request without
modification (for example, adding appropriate headers or SDP
values). However, the same request to a different server might be
successful.
6.4.1. 400 Bad Request
The request could not be understood due to malformed syntax. The
Reason-Phrase SHOULD identify the syntax problem in more detail, for
example, "Missing Sequence-Number header field".
6.4.2. 404 Not Found
The server has definitive information that the user does not exist
at the domain specified in the Request-URI. This status is also
returned if the domain in the Request-URI does not match any of the
domains handled by the recipient of the request.
6.4.3. 405 Method Not Allowed
The method specified in the Request-Line is understood, but not
allowed for the address identified by the Request-URI.
The response MUST include an Allow header field containing a list of
valid methods for the indicated address.
6.4.4. 406 Not Acceptable
The resource identified by the request is only able of generating
response entities that have content characteristics not acceptable
according to the Accept header field sent in the request.
Garcia Aranda Expires January 18, 2018 [Page 30]
Internet-Draft The Quality for Services Protocol July 2017
6.4.5. 408 Request Timeout
The server could not produce a response within a suitable amount of
time, and the client MAY repeat the request without modifications at
any later time
6.4.6. 413 Request Entity Too Large
The server is refusing to process a request because the request
entity-body is larger than the one that the server is willing or
able to process. The server MAY close the connection to prevent the
client from continuing the request.
6.4.7. 414 Request-URI Too Long
The server is refusing to process the request because the Request-
URI is longer than the one that the server accepts.
6.4.8. 415 Unsupported Media Type
The server is refusing to process the request because the message
body of the request is in a format not supported by the server for
the requested method. The server MUST return a list of acceptable
formats using the Accept, Accept-Encoding, or Accept-Language header
field, depending on the specific problem with the content.
6.4.9. 416 Unsupported URI Scheme
The server cannot process the request because the scheme of the URI
in the Request-URI is unknown to the server.
6.5. Server Failure 5xx
5xx responses are failure responses given when a server itself is
having trouble.
6.5.1. 500 Server Internal Error
The server encountered an unexpected condition that prevented it
from fulfilling the request. The client MAY display the specific
error condition and MAY retry the request after several seconds.
6.5.2. 501 Not Implemented
The server does not support the functionality required to fulfill
the request. This is the appropriate response when a Server does not
Garcia Aranda Expires January 18, 2018 [Page 31]
Internet-Draft The Quality for Services Protocol July 2017
recognize the request method and it is not capable of supporting it
for any user.
Note that a 405 (Method Not Allowed) is sent when the server
recognizes the request method, but that method is not allowed or
supported.
6.5.3. 503 Service Unavailable
The server is temporarily unable to process the request due to a
temporary overloading or maintenance of the server. The server MAY
indicate when the client should retry the request in a Retry-After
header field. If no Retry-After is given, the client MUST act as if
it had received a 500 (Server Internal Error) response.
A client receiving a 503 (Service Unavailable) SHOULD attempt to
forward the request to an alternate server. It SHOULD NOT forward
any other requests to that server for the duration specified in the
Retry-After header field, if present.
Servers MAY refuse the connection or drop the request instead of
responding with 503 (Service Unavailable).
6.5.4. 504 Server Time-out
The server did not receive a timely response from an external server
it accessed in attempting to process the request.
6.5.5. 505 Version Not Supported
The server does not support, or refuses to support, the Q4S protocol
version that was used in the request. The server is indicating that
it is unable or unwilling to complete the request using the same
major version as the client, other than with this error message.
6.5.6. 513 Message Too Large
The server was unable to process the request since the message
length exceeded its capabilities.
6.6. Global Failures 6xx
6xx responses indicate that a server has definitive information
about a particular policy not satisfied for processing the request.
Garcia Aranda Expires January 18, 2018 [Page 32]
Internet-Draft The Quality for Services Protocol July 2017
6.6.1. 600 session does not exist
The Session-Id is not valid
6.6.2. 601 quality level not allowed
The QOS level requested is not allowed for the pair client/server
6.6.3. 603 Session not allowed
The session is not allowed due to some policy (number of sessions
allowed for the server is exceeded, or the time band of the Q4S-
ALERT is not allowed for the pair client/server, etc)
6.6.4. 604 authorization not allowed
The policy server does not authorize the Q4S-ALERT quality session
improvement operation due to an internal or external reason.
7. Protocol
This section describes the measurement procedures, the SDP structure
of the Q4S messages, the different Q4S protocol phases and the
messages exchanged in them.
7.1. Protocol Phases
All elements of the IP network contribute to the quality in terms
of latency, jitter, bandwidth and packet loss. All these elements
have their own quality policies in terms of priorities, traffic
mode, etc. and each element has its own way to manage the quality.
The purpose of a quality connection is to establish an end-to-end
communication with enough quality for the application to function
flawlessly.
To monitor quality constraints of the application, four phases are
defined and can be seen in the following figure:
Garcia Aranda Expires January 18, 2018 [Page 33]
Internet-Draft The Quality for Services Protocol July 2017
+---------------------------------------------------------------+
| |
| |
| Handshake ---> Negotiation -+--> Continuity ----> Termination |
| A | (app start) | (app end) |
| | | A | A |
| | violated | violated | |
| | constraints | constraints | |
| | | | |_______| ____| |
| | | | +-------+ | |
| | | | | |
| +------+ +---------------------+ |
| |
+---------------------------------------------------------------+
Figure 5 Session lifetime phases.
o Handshake phase: in which the server is contacted by the client
and in the answer message the quality constraints for the
application is communicated embedded in an SDP.
o Negotiation phase: in which the quality of the connection is
measured in both directions (latency, jitter, bandwidth and
packet loss), and Q4S messages may be sent in order to alert if
the measured quality does not meet the constraints. This phase
is iterative until quality constraints are reached or the
session is cancelled after a number of measurement cycles with
consistent violation of the quality constraints. The number of
measurement cycles executed depends on the qos-level which is
incremented in each cycle until a maximum qos-level value is
reached. Just after reaching the quality requirements, Q4S
provides a simple optional mechanism using HTTP to start the
application.
o Continuity phase: in which quality is continuously measured. In
this phase the measurements MUST avoid disturbing the
application by consuming network resources. If quality
constraints are not met, the server stack will notify the
Actuator with an alert notification. If later the quality
improves, the server stack will notify the Actuator, in this
case with a recovery notification. After several alert
notifications with no quality improvements, the Q4S stack
should move to Termination phase.
Garcia Aranda Expires January 18, 2018 [Page 34]
Internet-Draft The Quality for Services Protocol July 2017
o Termination phase: in which the Q4S session is terminated. The
application may be closed too or may not start.
7.2. SDP Structure
The original goal of SDP was to announce necessary information for
the participants and multicast MBONE (Multicast Backbone)
applications. Right now, its use has been extended to the
announcement and the negotiation of multimedia sessions. The purpose
of Q4S is not to establish media stream sessions, but to monitor a
quality connection. This connection may be later used to establish
any type of session including media sessions; Q4S does not impose
any conditions on the type of communication requiring quality
parameters.
SDP will be used by Q4S to exchange quality constraints and will
therefore always have all the media attributes ("m") set to zero.
The SDP embedded in the messages is the container of the quality
parameters. As these may vary depending on the direction of the
communication (to and from the client) all quality parameters need
to specify the uplink and downlink values: / .
When one or both of these values are empty, it MUST be understood as
needing no constraint on that parameter and/or that direction.
The uplink direction MUST be considered as being the communication
from the client to the server. The downlink direction MUST be
considered as being the communication from the server to the client.
The SDP information can comprise all or some of the following
parameters shown in the example below. This is an example of an SDP
message used by Q4S included in the 200 OK response to a Q4S BEGIN
request.
Garcia Aranda Expires January 18, 2018 [Page 35]
Internet-Draft The Quality for Services Protocol July 2017
v=0
o=q4s-UA 53655765 2353687637 IN IP4 192.0.2.33
s=Q4S
i=Q4S parameters
t=0 0
a=qos-level:0/0
a=alerting-mode:Reactive
a= alert-pause:5000
a=public-address:client IP4 80.0.2.33
a=public-address:server IP4 198.51.100.58
a= latency:40
a= jitter:10/10
a= bandwidth:20/6000
a= packetloss:0.50/0.50
a=flow:app clientListeningPort TCP/10000-20000
a=flow:app clientListeningPort UDP/15000-18000
a=flow:app serverListeningPort TCP/56000
a=flow:app serverListeningPort UDP/56000
a=flow:q4s clientListeningPort UDP/55000
a=flow:q4s clientListeningPort TCP/55001
a=flow:q4s serverListeningPort UDP/56000
a=flow:q4s serverListeningPort TCP/56001
Notice that in this SDP example there are no measurement attributes,
these will only be included in the SDP body in Q4S-ALERT messages.
As quality constraints may be changed by applications at any time
during the Q4S session lifetime, any Q4S 200 OK response sent by the
server to the client in the Negotiation and Continuity phases could
also include an SDP body with the new quality requirements stated by
the applications from then on. Therefore, in response to any PING
request sent by the client to the server, the server could send a
Q4S 200 OK with an SDP message embedded that specifies new quality
constraints requested by the application.
7.2.1. "qos-level" attribute
The "qos-level" attribute contains the QoS level for uplink and
downlink. Default values are 0 for both directions. The meaning of
each level is out of scope of Q4S, but a higher level SHOULD
correspond to a better service quality.
The "qos-level" attribute may be changed during the session lifetime
raising or lowering the value as necessary following the network
measurements and the application needs.
Garcia Aranda Expires January 18, 2018 [Page 36]
Internet-Draft The Quality for Services Protocol July 2017
7.2.2. "alerting-mode" attribute
The "alerting-mode" attribute specifies the player in charge of
triggering Q4S alerts in case of constraint violation. There are two
possible values:
a) Q4S-aware-network: Q4S ALERT messages are triggered by the server
to the client. In this case the network is supposed to be Q4S
aware, and reacts by itself to these alerts.
b) Reactive: alert notifications are sent by the server stack to the
Actuator. In this case the network is not Q4S aware and a
specific node (Actuator) is in charge of triggering tuning
mechanisms., either on the network or in the application.
The "alerting-mode" attribute is optional and if not present
Reactive alerting mode is assumed.
7.2.3. "alert-pause" attribute
In the Q4S-aware-network scenario, the "alert-pause" attribute
specifies the amount of time (in milliseconds) the server waits
between consecutive Q4S ALERT messages sent to the client. In the
Reactive scenario, the "alert-pause" attribute specifies the amount
of time (in milliseconds) the server stack waits between consecutive
alert notifications sent to the Actuator. Measurements are not
stopped in Negotiation or Continuity Phases during this period of
time, but no Q4S ALERT messages or alert notifications are fired,
even with violated quality constraints, allowing either network
reconfigurations or application adjustments.
7.2.4. "recovery-pause" attribute
In the Q4S-aware-network scenario, the "recovery-pause" attribute
specifies the amount of time (in milliseconds) the server waits for
initiating the qos-level recovery process. Once the recovery process
has started, the "recovery-pause" attribute also states the amount
of time (in milliseconds) between consecutive Q4S-RECOVERY messages
sent by the server to the client (in the Q4S-aware-network
scenario), or between recovery notifications sent by the server
stack to the Actuator (in the Reactive scenario).
Garcia Aranda Expires January 18, 2018 [Page 37]
Internet-Draft The Quality for Services Protocol July 2017
7.2.5. "public-address" attributes
This attribute contains the public IP address of the client and the
server. The server fills these attributes with his own public IP
address and the public IP address of the first message received from
the client in the handshake phase.
The purpose of these attributes is to make available the addressing
information to network policy server or other external entities in
charge of processing Q4S-ALERT messages.
7.2.6. "latency" attribute
The maximum latency (considered equal for uplink and downlink)
tolerance are specified in the "latency" attribute, expressed in
milliseconds. In the Q4S-aware-network scenario, if the latency
constraints are not met, a Q4S-ALERT method will be sent to the
client. In the Reactive scenario, if the latency constraints are not
met, an alert notification will be sent to the Actuator. If the
"latency" attribute is not present or has a 0 value, no latency
constraints need to be met and no measurements MAY be taken.
7.2.7. "jitter" attribute
The maximum uplink and downlink jitter tolerance are specified in
the "jitter" attribute, expressed in milliseconds. In the Q4S-aware-
network scenario, if the jitter constraints are not met, a Q4S-ALERT
method will be sent to the client. In the Reactive scenario, if the
latency constraints are not met, an alert notification will be sent
to the Actuator. If "jitter" attribute is not present or has a 0
value, no jitter constraints need to be met and no measurements MAY
be taken.
7.2.8. "bandwidth" attribute
The minimum uplink and downlink bandwidth are specified in the
"bandwidth" attribute, expressed in kbps. In the Q4S-aware-network
scenario, if the bandwidth constraints are not met, a Q4S-ALERT
method will be sent to the client. In the Reactive scenario, an
alert notification will be sent to the Actuator. If "bandwidth"
attribute is not present or has a 0 value, no bandwidth constraints
need to be met and no measurements MAY be taken.
7.2.9. "packetloss" attribute
The maximum uplink and downlink packet loss tolerance are specified
in the "packetloss" attribute expressed in percentage (two decimal
Garcia Aranda Expires January 18, 2018 [Page 38]
Internet-Draft The Quality for Services Protocol July 2017
accuracy). In the Q4S-aware-network scenario, if the packetloss
constraints are not met, a Q4S-ALERT method will be sent to the
client. In the Reactive scenario, an alert notification will be sent
to the Actuator. If " packetloss" attribute is not present or has a
0 value, no packetloss constraints need to be met and no
measurements MAY be taken.
7.2.10. "flow" attributes
These attributes specify the flows (protocol, destination IP/ports)
of data over TCP and UDP ports to be used in uplink and downlink
communications.
Several "flow" attributes can be defined. These flows identify the
listening port (client or server), the protocol (TCP or UDP) (RFC
761 [8] and RFC 768 [9]) with the range of ports that are going to
be used by the application and, of course, by the Q4S protocol (for
quality measurements). All defined flows (app and q4s) will be
considered within the same quality profile, which is determined by
the qos-level attribute in each direction. This allows to assume
that measurements on q4s flows are the same experimented by the
application which is using app flows.
During negotiation and continuity phases the specified Q4S ports in
the "flow:q4s" attributes of SDP will be used for Q4S messages.
The Q4S flows comprise two UDP flows and two TCP flows (one uplink
and one downlink for each one) whereas application traffic MAY
consist of many flows, depending on its nature. The handshake phase
takes place through the Q4S Contact URI, using TCP port 80, for
example. However the negotiation and continuity phases will take
place on the specified Q4S ports (UDP and TCP) specified in the SDP.
Garcia Aranda Expires January 18, 2018 [Page 39]
Internet-Draft The Quality for Services Protocol July 2017
The "clientListeningPort" is a port in which the client listens for
server requests and MUST be used as origin port of client responses.
The "serverListeningPort" is a port in which server is listening for
incoming messages from the client. The origin port of server
responses may be different than "serverListeningPort" value.
If "clientListeningPort" is zero (a=flow:q4s clientListeningPort
TCP/0), the client MAY choose one randomly as per OS standard rules.
Client ports inside the SDP must always be matched against actual
received port values on the server side in order to deal with
NAT/NATP devices. If zero value or incorrect value is present,
server must set the value to the received origin port in the next
message with SDP (200 OK, ALERT and CANCEL messages).
7.2.11. Measurement attributes
These attributes contain the measurement procedure and the results
of the quality measurements.
Measurement parameters are included using the session attribute
"measurement". The first measurement parameter is the procedure. Q4S
provides a "default" procedure for measurements, but others like
RTP/RTCP might be used and defined later. This draft will only
define and explain the "default" procedure.
In the initial client request a set of measurement procedures can be
sent to the server for negotiation. One measurement procedure line
MUST be included in the SDP message for each proposed method. The
server MUST answer with only one line with the chosen procedure.
For each procedure, a set of values of parameters separated by ","
can be included in the same attribute line. The amount and type of
parameters depends on the procedure type.
In the following example the "default" procedure type is chosen:
a=measurement:procedure default(50/50,75/75,5000,40/80,100/256)
In the "default" procedure, the meaning of these parameters is:
o The first parameter is the interval of time (in milliseconds)
between PING requests during the negotiation phase. Uplink and
downlink values from the client's point of view are separated
by "/". This allows having different responsiveness values
depending on the control resources used in each direction.
Garcia Aranda Expires January 18, 2018 [Page 40]
Internet-Draft The Quality for Services Protocol July 2017
o The second parameter is the time interval (in milliseconds)
between PING requests during the continuity phase. Uplink and
downlink values are separated by "/". This allows having two
different responsiveness values depending on the control
resources used in each direction.
o The third parameter is the time interval to be used to measure
bandwidth during the negotiation phase..
o The fourth parameter indicates the window size for jitter and
latency calculations. Uplink and downlink values are separated
by "/".
o The fifth parameter indicates the window size for packet loss
calculations. Uplink and downlink values are separated by "/".
There are four more measurement attributes:
a=measurement:latency 45
a=measurement:jitter 3/12
a=measurement:bandwidth 200/9800
a=measurement:packetloss 0.00/1.00
The latency, jitter, bandwidth and packetloss measurement attributes
contain the values measured for each of these quality parameters in
uplink and downlink directions. Notice that latency is considered
equal for uplink and downlink directions. Quality parameter values
in these measurement attributes provide a snapshot of the quality
reached and MUST only be included in Q4S-ALERT messages in the SDP
body such that they can be protected from malicious attacks as these
alerts include a signature of the SDP body in the header. The rest
of messages will include the measured values in the Measurements
header.
7.3. Measurements
This section describes the way quality parameters are measured as
defined by the "default" procedure. Measurements MUST be taken for
any quality parameter with constraints, that is, specified in the
SDP attributes with non-zero values. For non-present attributes
measurements MAY be omitted.
Garcia Aranda Expires January 18, 2018 [Page 41]
Internet-Draft The Quality for Services Protocol July 2017
7.3.1. Latency
Latency measurements will be performed if the latency attribute
and/or the application latency attribute are present and with non-
zero values.
Q4S defines a PING method in order to exchange packets between the
client and the server. Based on this PING exchange the client and
the server are able to calculate the round-trip time (RTT). The RTT
is the sum of downlink latency (normally named "reverse latency")
and uplink latency (normally named "forward latency").
At least 255 samples of RTT MUST be taken by the client and server.
As the forward and reverse latencies are impossible to measure,
client and server will assume that both latencies are identical
(symmetric network assumption). The latency will therefore be
calculated as the statistical median value of all the RTT samples
divided by 2.
7.3.2. Jitter
Jitter measurements will be performed if the jitter attribute and/or
the application jitter attribute are present and with non-zero
values.
The jitter can be calculated independently by the client and by the
server. The downlink jitter is calculated by the client taking into
account the time interval between PING requests as defined by the
measurement procedure attribute in the first or second parameter
depending on the Q4S protocol phase. The client and the server MUST
send these PING requests at the specified intervals. The client
measures the downlink jitter whereas the server measures the uplink
jitter. Note that PING responses are not taken into account when
calculating jitter values.
Every time a PING request message is received by an endpoint (either
server or client), the corresponding jitter value is updated using
the Statistical Jitter value calculated on the first 255 packets
received using the arithmetic mean of the absolute values of elapsed
times.
Each endpoint sends a PING periodically with a fixed interval, each
value of "elapsed time" (ET) should be very close to this interval.
If a PING message is lost, the elapsed time value is doubled.
Identifying lost PING messages, however, is not an issue because all
Garcia Aranda Expires January 18, 2018 [Page 42]
Internet-Draft The Quality for Services Protocol July 2017
PING messages are labeled with a Sequence-Number header. Therefore
the receiver can discard this elapsed time value.
In order to have the first jitter sample, the receiver MUST wait
until it receives 3 PING requests, because each ET is the time
between two PINGs and a Jitter needs at least two ET.
The client measures the values of RTT and downlink jitter and the
server measures RTT and uplink jitter, but all measurements are
shared with the counterpart by means of "Measurements" header of
PING message.
7.3.3. Bandwidth
Bandwidth measurements will be performed if the bandwidth attribute
and/or the application bandwidth attribute is present and with non-
zero values.
In order to measure the available bandwidth, both the client and the
server MUST start sending BWIDTH messages simultaneously using the
UDP control ports exchanged during the handshake phase in the SDP
message, at the needed rate to verify the availability of the
bandwidth constraint in each direction using messages of 1 Kbyte or
more in length. The messages are sent during the period of time
defined in the third parameter of the SDP measurement default
procedure attribute in millisecond units.
a=measurement:procedure default(50/50,75/75,5000,256/256,256/256)
Garcia Aranda Expires January 18, 2018 [Page 43]
Internet-Draft The Quality for Services Protocol July 2017
+------------------------------------------------+
| Rate |
| A |
| | |
|downlink rate-|-------------------+ time |
| 0 1 2 3 4 5 (sec.) |
| |
+------------------------------------------------+
Figure 6 Bandwidth and packet loss measurements.
The goal of these measurements is not to identify the available
bandwidth of the communication path but to determine if the required
bandwidth is available, meeting the application's constraints.
Therefore, the requested bandwidth MUST be measured sending only the
highest bit rate required by the bandwidth attribute.
When measuring bandwidth, all BWIDTH requests sent MUST be 1
kilobyte in length (UDP payload length), and MUST include a
Sequence-Number header with a sequential number starting at 0. The
Sequence-Number MUST be incremented by 1 with each BWIDTH packet
sent. If any measurement stage needs to be repeated, the sequence
number MUST start at zero again. BWIDTH requests MUST NOT be
answered. Examples:
Garcia Aranda Expires January 18, 2018 [Page 44]
Internet-Draft The Quality for Services Protocol July 2017
Client message:
=========================
BWIDTH q4s://www.example.com Q4S/1.0
User-Agent: q4s-ua-experimental-1.0
Session-Id: 53655765
Sequence-Number: 0
Content-Type: text
Content-Length: XXXX
Measurements: l=22, j=10, pl=0.00, bw=3000
aaaaaaaaaaaaa ( to complete 1024 bytes UDP payload length)
=========================
The client MUST send BWIDTH packets to the server to allow the
server to measure the uplink bandwidth. The server MUST send BWIDTH
packets to the client to allow the client to measure the downlink
bandwidth.
Server message:
=========================
BWIDTH q4s://www.example.com Q4S/1.0
Session-Id: 53655765
Sequence-Number: 0
Content-Type: text
Content-Length: XXXX
Measurements: l=22, j=7, pl=0.00, bw=200
aaaaaaaaaaaaa ( to complete 1024 bytes UDP payload length)
=========================
7.3.4. Packet loss
Packet loss and bandwidth are measured simultaneously using the
BWIDTH packets sent by both the client and the server. Because the
BWIDTH packets contain a Sequence-Number header incremented
sequentially with each sent packet, lost packets can be easily
identified. The lost packets have to be counted during the
measurement time.
Garcia Aranda Expires January 18, 2018 [Page 45]
Internet-Draft The Quality for Services Protocol July 2017
7.4. Handshake Phase
The first phase consists of a Q4S BEGIN method issued from the
client to the server.
The first Q4S message MUST have a special URI (RFC 3986 [4]), which
forces the use of the Q4S protocol if it is implemented in a
standard web browser.
This URI, named "Contact URI", is used to request the start of a
session. Its scheme MUST be:
"q4s:" "//" host [":" port] [path["?" query]
Optionally, the client can send the desired quality parameters
enclosed in the body of the message as an SDP document. The server
MAY take them into account when building the answer message with the
final values in the SDP body, following a request / response schema
(RFC 3464 [5]).
If the request is accepted, the server MUST answer it with a Q4S 200
OK message, which MUST contain an SDP body (RFC 4566 [2]) with the
assigned session id (embedded in the "o" SDP parameter), the IP
addresses to be used, the flow ports to be used, the measurement
procedure to be followed and information about the required quality
constraints. Additionally, the alerting-mode and alert-pause time
parameters may be included. Q4S responses should use the protocol
designator "Q4S/1.0".
After these two messages are exchanged, the first phase is
completed. The quality parameter thresholds have been sent to the
client. The next step is to measure the actual quality of the
communication path between the client and the server and alert if
the SLA is being violated.
+------------------------------------------------+
| |
| Client Server |
| |
| ------- Q4S BEGIN ------------> |
| |
|
Internet-Draft The Quality for Services Protocol July 2017
Example of Client Request and Server Answer:
Client Request:
=========================
BEGIN q4s://www.example.com Q4S/1.0
Content-Type: application/sdp
User-Agent: q4s-ua-experimental-1.0
Content-Length: 142
(SDP not shown)
=========================
Server Answer:
=========================
Q4S/1.0 200 OK
Date: Mon, 10 Jun 2010 10:00:01 GMT
Content-Type: application/sdp
Expires: 3000
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Length: 131
(SDP not shown)
=========================
The headers used are explained in section 4.3.
7.5. Negotiation phase
The negotiation phase is in charge of measuring the quality
parameters and verifying that the communication paths meet the
required quality constraints on both directions as specified in the
SDP body.
The measured parameters will be compared with the quality
constraints specified in the SDP body. If the quality session is
compliant with all the quality constraints the application can
start.
Garcia Aranda Expires January 18, 2018 [Page 47]
Internet-Draft The Quality for Services Protocol July 2017
o If the quality constraints are not met, a higher quality
service level will be demanded. Depending on the scenario, this
quality upgrade will be managed as follows: In the Q4S-aware-
network scenario: a Q4S-ALERT method will be triggered by the
server to the client and the client will answer with the same
Q4S-ALERT method. After receiving the same Q4S-ALERT from the
counterpart, no other alerts will be triggered by the server
during the "alert-pause" period of time, in order to allow the
network to react, but measurements will continue to be taken to
achieve early detection of improved network quality conditions
and a fast application start.
o In the Reactive scenario: an alert notification will be sent by
the server stack to the Actuator, and the Actuator will answer
with an alert acknowledgement. After receiving the alert
acknowledgement from the Actuator, the server stack will not
send other alert notifications during the "alert-pause" period
of time, in order to allow the Actuator to react and trigger
actions on the application or on the policy server, but
measurements will continue to be taken to achieve early
detection of improved network quality conditions and a fast
application start.
In both scenarios stated above, if after several measurement cycles,
the network constraints cannot be met the quality session is
terminated. Concretely when under all possible actions taken by
Actuator the quality remains below requirements, the session must be
terminated.
The steps to be taken in this phase depend on the measurement
procedure exchanged during the handshake phase. This document only
describes the "default" procedure, but others can be used, like
RTP/RTCP (RFC 3550 [10]).
Measurements of latency and jitter are done calculating the
differences in arrival times of packets and can be achieved with
little bandwidth consumption. The bandwidth measurement, on the
other hand, involves higher bandwidth consumption in both directions
(uplink and downlink).
To avoid wasting unnecessary network resources these two types of
measurements will be performed in two separate stages. If the
required latencies and jitters cannot be reached, it makes no sense
to waste network resources measuring bandwidth. In addition, if
achieving the required latency and jitter thresholds implies
upgrading the quality session level, the chance of obtaining
compliant bandwidth measurements without retries is higher, saving
Garcia Aranda Expires January 18, 2018 [Page 48]
Internet-Draft The Quality for Services Protocol July 2017
network traffic again. Therefore, the default procedure, determines
that the measurements are taken in two stages:
o Stage 0: Measurement of latencies, jitters and packet loss
o Stage 1: Measurement of bandwidths and packet loss
Notice that packet loss can be measured in both stages, as all
messages exchanged include a sequence-number header that allows for
easy packet loss detection.
The client starts the negotiation phase sending a READY request
using the TCP Q4S ports defined in the SDP. This READY request
includes a "Stage" header that indicates the measurement stage.
If either jitter, latency or both are specified, the negotiation
phase begins with the measurement of latencies and jitters (stage
0). If none of those attributes are specified, stage 0 is skipped.
7.5.1. Stage 0: Measurement of latencies and jitters
The Stage 0 MUST start with a synchronization message exchange
initiated with the client's READY message.
Client request, READY message:
=========================
READY q4s://www.example.com Q4S/1.0
Stage: 0
Session-Id: 53655765
User-Agent: q4s-ua-experimental-1.0
Content-Length: 0
=========================
Server Response:
=========================
Q4S/1.0 200 OK
Session-Id: 53655765
Stage:0
Content-Length: 0
=========================
Garcia Aranda Expires January 18, 2018 [Page 49]
Internet-Draft The Quality for Services Protocol July 2017
This triggers the exchange of a sequence of PING requests and
responses that will lead to the calculation of RTT (latency), jitter
and packet loss.
After receiving 200 OK, the client must send the first PING message
and the server will wait to send PINGs until the reception of this
first client PING.
Client and server MUST send PING requests to each other. The
Sequence-Number header of the first PING MUST be set to 0. Client
and server will manage their own sequence numbers.
+------------------------------------------------+
| |
| Client Server |
| |
| --------- Q4S READY 0 ---------> |
| |
| |
| --------- Q4S PING ------------> |
| |
|
Internet-Draft The Quality for Services Protocol July 2017
Client Request:
=========================
PING q4s://www.example.com Q4S/1.0
Session-Id: 53655765
Sequence-Number: 0
User-Agent: q4s-ua-experimental-1.0
Measurements: l=22, j=12, pl=0.20, bw=
Content-Length: 0
=========================
Server Response:
=========================
Q4S/1.0 200 OK
Session-Id: 53655765
Sequence-Number: 0
Content-Length: 0
=========================
The function of the PING method is similar to the ICMP echo request
message. The server MUST answer as soon as it receives the message.
Both endpoints MUST send Q4S PING messages with the periodicity
specified in the first parameter of SDP measurement procedure
attribute, using always the same UDP ports and incrementing the
Sequence-Number with each message.
In the following example, the SDP measurement procedure attribute,
this value is 50 milliseconds (from the client to the server) and
60ms (from the server to the client).
a=measurement:procedure default(50/60,50/50,5000,256/256,256/256)
They MUST NOT wait for a response to send the next PING request. The
"Sequence-Number" header value is incremented sequentially and MUST
start at zero. If this stage is repeated, the initial Sequence-
Number MUST start at zero again.
All PING requests MUST contain a "Measurements" header, with the
values of the latency, jitter and packet loss measured by each
entity up to that moment. The client will send its measurements to
the server and the server his measurements to the client. Example:
Measurements: l=22, j=13, pl=0.10, bw=
Where l stands for latency, j for jitter, pl for packetloss and bw
for bandwidth. The bandwidth value is omitted, as it is not measured
at this stage.
Garcia Aranda Expires January 18, 2018 [Page 51]
Internet-Draft The Quality for Services Protocol July 2017
Optionally the PING request can include a "Timestamp" header, with
the time in which the message has been sent. In case the header is
present, the server MUST include the header in the response without
changing the value.
A minimum number of PING messages MUST be exchanged in order to be
able to measure latency, jitter and packet-loss with certain
accuracy (at least 256 samples are recommended to get a accurate
packet loss measurement). Both the client and the server calculate
the respective measured parameter values. The mechanisms to
calculate the different parameters are described in section 7.3.
At the end of this stage 0, there are three possibilities:
o The latency, jitter and packet loss constraints are reached in
both directions
o The latency, jitter and packet loss constraints are not reached
in one or both directions
In the first case, Stage 0 is finished. Client and server are ready
for Stage 1: bandwidth and packet loss measurement. The client moves
to stage 1 by sending a READY message including the header "Stage:
1".
If the bandwidth constraints are empty or with value zero, the
negotiation phase MUST terminate and both client and server may
initiate the Continuity Phase. In this case client moves to
Continuity phase by sending a READY message including the header
"Stage: 2".
The second case, in which one or more quality constraints have not
been met, is detailed in section 7.5.4. Quality constraints not
reached.
7.5.2. Stage 1: Measurement of bandwidth and packet loss
This stage begins in a similar way to stage 0, sending a READY
request over TCP. This READY message "Stage" header value is 1. The
server answers with a Q4S 200 OK message to synchronize the
initiation of the measurements.
Garcia Aranda Expires January 18, 2018 [Page 52]
Internet-Draft The Quality for Services Protocol July 2017
+------------------------------------------------+
| |
| Client Server |
| |
| --------- Q4S READY 1 -----------> |
| |
| |
|
Internet-Draft The Quality for Services Protocol July 2017
o The bandwidth and packet loss constraints are reached in both
directions
o The bandwidth and packet loss constraints are not reached in
one both directions.
In the first case, Stage 1 is finished. Client and server are ready
for Continuity phase. The client moves to this phase by sending a
READY message including the header "Stage: 2". The server answer
MUST be 200 OK.
+------------------------------------------------+
| |
| Client Server |
| |
| --------- Q4S READY 2 --------------> |
| |
| |
| (Application starts) |
| |
+------------------------------------------------+
Figure 10 Trigger the application using HTTP URI
Garcia Aranda Expires January 18, 2018 [Page 54]
Internet-Draft The Quality for Services Protocol July 2017
Client Request:
=========================
READY q4s://www.example.com Q4S/1.0
User-Agent: q4s-ua-experimental-1.0
Stage: 2
Session-Id: 53655765
Content-Length: 0
=========================
Server Answer:
=========================
Q4S/1.0 200 OK
Date: Mon, 10 Jun 2010 10:00:01 GMT
Session-Id: 53655765
Trigger-URI: http://www.example.com/app_start
Expires: 3000
Content-Type: application/sdp
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Length: 131
(SDP not shown)
=========================
If the "Trigger-URI" header is present, the client SHOULD send an
HTTP request to this URI.
The second case, with violated network constraints is explained in
7.5.4 Quality constraints not reached.
7.5.3. Quality constraints not reached
After finishing Stage 1 of the Negotiation phase, the client and the
server have each other measured parameter values as these have been
exchanged in the "Measurements" headers of the PING and BWIDTH
messages. If there is one or more parameters that do not comply with
the uplink or downlink application constraints required both the
server and the client are aware of it.
Garcia Aranda Expires January 18, 2018 [Page 55]
Internet-Draft The Quality for Services Protocol July 2017
If there is any quality parameter that does not meet the uplink or
downlink quality constraints specified in the SDP message, two
scenarios are possible depending on the specified alerting-mode (if
not present, default value is "Reactive" alerting mode):
a) Q4S-aware-network alerting mode: the server MUST send a Q4S-ALERT
message to the client including the digital signature header, and
the client MUST answer with the same Q4S-ALERT message. The
Signature header contains the signed hash value of the SDP body
in order to protect all the SDP the data and therefore it MUST
contain the measurement parameters in the body.
Garcia Aranda Expires January 18, 2018 [Page 56]
Internet-Draft The Quality for Services Protocol July 2017
Server request
=========================
Q4S-ALERT q4s://www.example.com Q4S/1.0
Host: www.example.com
User-Agent: q4s-ua-experimental-1.0
Session-Id: 53655765
Content-Type: application/sdp
Content-Length: 142
v=0
o=q4s-UA 53655765 2353687637 IN IP4 192.0.2.33
s=Q4S
i=Q4S parameters
t=0 0
a=qos-level:1/2
a=alerting-mode: Q4S-aware-network
a= alert-pause:5000
a=public-address:client IP4 80.0.2.33
a=public-address:server IP4 198.51.100.58
a= latency:40
a= jitter:10/10
a= bandwidth:20/6000
a= packetloss:0.50/0.50
a=flow:app downlink TCP/10000-20000
a=flow:app uplink TCP/56000
a=flow:q4s downlink UDP/55000
a=flow:q4s downlink TCP/55001
a=flow:q4s uplink UDP/56000
a=flow:q4s uplink TCP/56001
a=measurement:procedure default(50/50,50/50,5000,256/256,256/256)
a=measurement:latency 30
a=measurement:jitter 6/4
a=measurement:bandwidth 200/4000
a=measurement:packetloss 0.20/0.33
=========================
At this point, both client and server keep on measuring but without
sending new Q4S ALERT messages during the "alert-pause"
milliseconds.
b) Reactive alerting mode: the server stack MUST send an alert
notification to the Actuator, and the Actuator MUST answer with
Garcia Aranda Expires January 18, 2018 [Page 57]
Internet-Draft The Quality for Services Protocol July 2017
an acknowledgement to the received alert notification. The alert
notification sent to the Actuator by the server stack doesn't
follow Q4S message style but should have all the information the
Actuator will need for the actions to be taken, which will be
implementation dependent.
At this point, during Negotiation phase, both client and server keep
on measuring without sending new alert notifications to the Actuator
during the "alert-pause" milliseconds specified in the SDP. This
way, both client and server will detect any improvement in network
conditions as soon as the network reacts. The application can start
as soon as the number of measurements indicated in the measurement
procedure attribute indicates that the quality parameters are met.
Same applies to Continuity phase: the measurement dialog between
client and server must not be interrupted by any possible ALERT
message.
7.5.3.1. Actuator role
Actuator receives notifications of unmet requirements from Q4S
server stack, and act over the application or over the network
policy server, according with certain logic out of scope of this
protocol.
The Actuator logic activates mechanisms at application level or/and
network level based on a quality level dictionary, in which each
level meaning is implementation dependent and each level involve
different actions based on rules to keep certain user experience
quality.
The type of actions that an actuator can take at application level
are application dependent and may involve:
o Reduction of application functionalities, such as limitation of
application speed or application options.
o Reduction of application resources usage, such as reduction of
frames per second in a video app or any other parameter
modification in order to adapt to network conditions.
Apart from actuate at application level, the actuator may act at
network level if a network policy server is available.
Garcia Aranda Expires January 18, 2018 [Page 58]
Internet-Draft The Quality for Services Protocol July 2017
7.5.3.2. Policy server role
A network policy server may be part of the reactive scenario and it
is in charge of managing network quality provision. Network policy
server may implement all or some of these features (but not
exclusive to):
o Server validation in terms of quality constraints.
o Authentication (Signature validation) and security (block
malicious clients)
o Policy rules (following rules are only examples):
- Maximum quality level allowed for the ACP
- Time bands allowed for providing quality sessions
- Number of simultaneous quality sessions allowed
- Maximum time used by allowed quality sessions
- Etc.
If any of the policy rules fail, a Q4S-ALERT message must be
answered by a 6XX error, indicating the cause.
7.5.4. QoS Level changes
If any constraint was violated, client or server (depending on
alerting mode) MAY trigger a Q4S-ALERT asking for higher qos-level
attribute. The maximum qos-level allowed is 9, both uplink and
downlink.
If the qos-level has reached the maximum value for downlink or
uplink without matching the constraints, then a CANCEL request MUST
be sent by the client using the TCP port determined in the handshake
phase in order to release the session. In reaction to the reception
of the CANCEL request, the server MUST send a CANCEL request too. If
no CANCEL request is received, the expiration time cancels the
session at server side.
Garcia Aranda Expires January 18, 2018 [Page 59]
Internet-Draft The Quality for Services Protocol July 2017
Client Request:
=========================
CANCEL q4s://www.example.com Q4S/1.0
User-Agent: q4s-ua-experimental-1.0
Session-Id: 53655765
Content-Type: application/sdp
Content-Length: 142
(SDP not shown)
=========================
Server Request in reaction to Client Request:
=========================
CANCEL q4s://www.example.com Q4S/1.0
Session-Id: 53655765
Expires: 0
Content-Type: application/sdp
Signature: 6ec1ba40e2adf2d783de530ae254acd4f3477ac4
Content-Length: 131
(SDP not shown)
=========================
7.6. Continuity phase
During the negotiation phase, latency, jitter, bandwidth and packet
loss have been measured. During the continuity phase bandwidth will
not be measured again because bandwidth measurements may disturb
application performance.
This phase is supposed to be executed at the same time as the real
time application is being used.
This draft only covers the default procedure. The continuity
operation with default procedure is based on a sliding window of
samples. The number of samples involved in the sliding window may be
different for jitter and latency than for packet-loss calculations
according to the fifth and sixth parameters of the measurement
procedure attribute. In this example, the jitter and latency sliding
window comprises 40 samples whereas the size of the packet-loss
sliding window is 100 samples:
a=measurement:procedure default(50/50,75/75,5000,40/40,100/100)
Garcia Aranda Expires January 18, 2018 [Page 60]
Internet-Draft The Quality for Services Protocol July 2017
In addition, the sizes of these windows are configurable per
direction: uplink and downlink values may differ.
PING requests are sent continuously (in both directions) and when
the Sequence-Number header reaches the maximum value, the client
continues sending PING messages with the Sequence-Number header
starting again at zero. When the server PING Sequence-Number header
reaches the maximum value, it does the same, starting again from
zero.
On the client side, the measured values of downlink jitter, downlink
packet loss and latency are calculated using the last samples,
discarding older ones, in a sliding window schema.
+--------------------------------------------------+
| |
| 55 56 57 . . . 253 254 255 0 1 2 . . . 55 56 |
| A A |
| | | |
| +-----------------------------------+ |
| |
+--------------------------------------------------+
Figure 11 Sliding samples window
Only if the server detects that the measured values (downlink or
uplink jitter, packet loss or latency) are not reaching the quality
constraints, a Q4S ALERT is triggered and sent either to the client
or to the Actuator, depending on the alerting mode, and the alert-
pause timer is started.
In Q4S-aware-network alerting mode, if the client receives a Q4S
ALERT message, it MUST answer sending the Q4S ALERT request message
back to the server including the SDP (with its corresponding digital
signature).
Both client and server will keep performing measurements but no
other Q4S ALERT message MUST be sent during "alert-pause"
milliseconds. The operations needed to act on the network and the
agents in charge of them are out of scope of this draft.
Garcia Aranda Expires January 18, 2018 [Page 61]
Internet-Draft The Quality for Services Protocol July 2017
+------------------------------------------------+
| |
| Client Server |
| |
| ... |
| ----------- PING ----------> |
| |
| |
| ----------- PING ----------> |
| |
| ... |
| |
+------------------------------------------------+
Figure 12 Continuity in Q4S-aware-network alerting mode
In the Reactive scenario, if the server detects that the measured
values (downlink or uplink jitter, packet loss or latency) are not
reaching the quality constraints, an alert notification is triggered
and sent to the Actuator. The Actuator must then answer to the
server stack with an alert acknowledgement
The measurement dialog between the client and the server must not be
interrupted by any possible ALERT message.
Garcia Aranda Expires January 18, 2018 [Page 62]
Internet-Draft The Quality for Services Protocol July 2017
+------------------------------------------------+
| |
| Client Server Actuator |
| ... |
| --- PING ----------> |
| |
| |
| --- PING ----------> |
| ... |
| |
+------------------------------------------------+
Figure 13 Continuity in Reactive alerting mode
7.7. Termination Phase
The Termination phase is end point for the established Q4S session
that is reached in the following cases:
. A CANCEL message has been received. The client sends a CANCEL
message due to the impossibility of the network to meet the
required quality constraints. The client and server application
will be notified by the respective Q4S stack.
. Session expires: if after the Expires time no client or server
activity is detected, that end cancels the session.
. A BEGIN message has been received by the server. The pre-
existing Q4S quality session is cancelled and a new session
will be initiated.
The meaning of Termination phase in terms of release of resources or
accounting is application dependent and out of scope of the Q4S
protocol.
In Reactive alerting mode, Q4S CANCEL messages received by the Q4S
server must cause the sending of cancel notifications sent from the
server stack to the Actuator in order to release possible assigned
resources for the session.
Garcia Aranda Expires January 18, 2018 [Page 63]
Internet-Draft The Quality for Services Protocol July 2017
7.7.1. Sanity check of Quality sessions
A session may finish due to several reasons (client shutdown, client
CANCEL request, constraints not reached, etc), and any session
finished MUST release the assigned resources.
In order to release the assigned server resources for the session,
the "Expires" header indicates the maximum interval of time without
exchanging any Q4S message.
7.8. Dynamic constraints and flows
Depending on the nature of the application, the quality constraints
to be reached may evolve, changing some or all quality constraint
values in any direction.
The client MUST be able to deal with this possibility. When the
server sends an SDP document attached to a response (200 OK, or Q4S-
ALERT, etc), the client MUST take all the new received values,
overriding any previous value in use.
The dynamic changes on the quality constraints can be as a result of
two possibilities:
o The application communicates to the Q4S server a change in the
constraints. In this case the application requirements can
evolve and the Q4S server will be aware of them.
o The application uses TCP flows. In that case, in order to
guarantee a constant throughput, the nature of TCP behavior
forces the use of a composite constraint function, which
depends on RTT, packet loss and window control mechanism
implemented in each TCP stack.
TCP throughput can be less than actual bandwidth if the
Bandwidth-Delay Product (BDP) is large or if the network suffers
from a high packet loss rate. In both cases, TCP congestion control
algorithms may result in a suboptimal performance.
Different TCP congestion control implementations like Reno [14],
High Speed TCP (RFC 3649 [15]), CUBIC [16], Compound TCP (CTCP
[17]), etc. reach different throughputs under the same network
conditions of RTT and packet loss. In all cases, depending on the
Garcia Aranda Expires January 18, 2018 [Page 64]
Internet-Draft The Quality for Services Protocol July 2017
RTT measured value, the Q4S server could change dynamically the
packetloss constraints (defined in SDP) in order to make possible to
reach a required throughput or vice versa (use packetloss
measurement to change dynamically latency constraints).
A general guideline to calculate the packetloss constraint and RTT
constraint consists in approximating the throughput using a
simplified formula, which should take into account the TCP stack
implementation of the receiver, in addition to RTT and packet loss:
Th= Function( RTT, packet loss, ...)
Then, depending on RTT measured values, set dynamically the
packetloss constraint.
It is possible to easily calculate a worst-case boundary for the
Reno algorithm, which should ensure for all algorithms that the
target throughput is actually achieved. Except that, high-speed
algorithms will then have even a larger throughput, if more
bandwidth is available.
For the Reno algorithm, the Mathis' formula may be used [15] for the
upper bound on the throughput:
Th <= (MSS/RTT)*(1 / sqrt{p})
In absence of packet loss, a practical limit for the TCP throughput
is the receiver_window_size divided by the round-trip time. However,
if the TCP implementation uses a window scale option, this limit can
reach the available bandwidth value.
7.9. Qos-level upgrade and downgrade operation
Each time the server detects violation of constraints, the alert
mechanism is triggered, the alert-pause timer is started and the
qos-level is increased. When this happens repeatedly and the qos-
level reaches its maximum value (value 9), the session is cancelled.
But when the violation of constraints stops before reaching qos-
level maximum value, the recovery mechanism allows for the qos-level
upgrade gradually.
Following, this downgrade and upgrade of qos-level is explained with
an example:
1. A Q4S session is initiated successfully with qos-level=0.
Garcia Aranda Expires January 18, 2018 [Page 65]
Internet-Draft The Quality for Services Protocol July 2017
2. During the continuity phase, violation of constraints is
detected; qos-level is increased to 1, a Q4S-ALERT is sent by
the server to the client and alert-pause timer is started.
3. Alert-pause timer expires and still violation of constraints
is detected; qos-level is increased to 2, a Q4S-ALERT is sent
by the server to the client and alert-pause timer is started.
4. Alert-pause timer expires but violation of constraints has
stopped; recovery-pause is started.
5. Recovery-pause timer expires and no violation of constraints
has been detected meanwhile; qos-level is decreased to 1, a
Q4S-RECOVERY is sent by the server to the client and recovery-
pause timer is started again.
6. Recovery-pause timer expires again and no violation of
constraints has been detected meanwhile; qos-level is decreased
to 0 and a Q4S-RECOVERY is sent by the server to the client;
recovery-pause timer is not started this time as qos-level has
reached its initial value.
When the network configuration allows for the possibility of
managing Q4S flows and application flows independently (either is a
network-based QoS or a Q4S aware network), the qos-level downgrade
process could be managed more efficiently using a strategy that
allows for carrying out qos-level downgrades excluding app flows
from SDP dynamically. The Q4S flows would be downgraded to allow for
measurements on a lower quality level without interference of the
application flows. A Q4S client MUST allow this kind of SDP
modifications by the server.
Periodically (every several minutes, depending on the
implementation) a Q4S-ALERT could be triggered, in which the level
is downgraded for Q4S flows, excluding application flows from the
embedded SDP of that request.
This mechanism allows to measure at lower levels of quality while
application flows continue using a higher qos level value.
o If the measurements in the lower level meet the quality
constraints, then a Q4S-RECOVERY message to this lower qos-
level may be triggered, in which the SDP includes the
application flows in addition to Q4S flows.
Garcia Aranda Expires January 18, 2018 [Page 66]
Internet-Draft The Quality for Services Protocol July 2017
o If the measurements in the lower level do not meet the
constraints, then a new Q4S-ALERT to the previous qos-level
MUST be triggered, in which the SDP includes only the Q4S
flows.
+------------------------------------------------+
| |
| qos-level |
| A |
| | |
| 4| |
| | |
| 3| +------+ |
| | | | |
| 2| +----+ +----+ +--- |
| | | | | |
| 1| +----+ +-----+ |
| | | |
| 0+---+---------------------------------> time |
| |
+------------------------------------------------+
Figure 14 Possible evolution of qos-level
This mechanism avoids the risk of disturbing the application, while
the measurements are being run in lower levels. However, this
optional optimization of resources MUST be used carefully.
The chosen period to measure a lower qos level is implementation
dependent. Therefore it is not included as a measurement procedure
parameter. It is recommended to use a large value, such as 20
minutes.
8. General User Agent behavior
8.1. Roles in peer to peer scenarios
In order to allow peer to peer applications, a Q4S User Agent (UA)
MUST be able to assume both client and server role. The role assumed
depends on who sends the first message.
In a communication between two UAs, the UA that sends the Q4S BEGIN
request in the first place, for starting the handshake phase, shall
assume the client role.
Garcia Aranda Expires January 18, 2018 [Page 67]
Internet-Draft The Quality for Services Protocol July 2017
If both UASs send the BEGIN request at the same time, they will wait
for a random time to restart again.
Otherwise, an UA may be configured to act only as server (e.g.,
content provider's side).
+-----------------------------------------------+
| |
| UA(Client) UA(Server) |
| |
| -------- Q4S BEGIN -------------> |
| |
|
Internet-Draft The Quality for Services Protocol July 2017
8.3. General client behavior
A Q4S Client has different behaviors. We will use letters X,Y,Z to
designate each different behavior (follow the letter bullets in the
figure below).
X) When it sends messages over TCP (methods BEGIN, READY, Q4S-
ALERT, Q4S-RECOVERY and CANCEL) it behaves strictly like a state
machine that sends requests and waits for responses. Depending on
the response type it enters in a new state.
When it sends UDP messages (methods PING and BWIDTH), a Q4S client
is not strictly a state machine that sends messages and waits for
responses because:
Y) At latency, jitter and packet loss measurement, the PING
requests are sent periodically, not after receiving the response
to the previous request. In addition, the client MUST answer the
PING requests coming from the server, therefore the client assumes
temporarily the role of a server.
Z) At bandwidth and packet loss measurement stage, the client does
not expect to receive responses when sending BWIDTH requests to
the server. In addition, it MUST receive and process all server
messages in order to achieve the downlink measurement.
The Q4S-ALERT and CANCEL may have a conventional answer if an error
is produced, otherwise the corresponding answer is formatted as a
request message.
+-----------+------------------------+-----------+-----------+
| Handshake | Negotiation |Continuity |Termination|
| Phase | Phase | Phase | Phase |
| | | | |
| X ---------> Y --> X --> Z --> X ---> Y --> X ---> X |
| | A | A | | A | | |
| | | | | | | | | | |
| | +-----+ +-----+ | +-----+ | |
| | | | |
+------------------------------------------------+-----------+
Figure 16 Phases & client behaviors.
Garcia Aranda Expires January 18, 2018 [Page 69]
Internet-Draft The Quality for Services Protocol July 2017
8.3.1. Generating requests
A valid Q4S request formulated by a Client MUST, at a minimum,
contains the following header fields:
o If no SDP is included: the header Session-Id and Sequence-
Number are mandatory.
o If SDP is included: Session-Id is embedded into SDP, therefore
the inclusion of Session-Id header is optional but if present
must have the same value. Measurements are embedded into the
SDP only for Q4S-ALERT messages in order to be signed.
At any time, if the server sends a new SDP with updated values,
client MUST take it into account.
8.4. General server behavior
If a server does not understand a header field in a request (that
is, the header field is not defined in this specification or in any
supported extension), the server MUST ignore that header field and
continue processing the message.
The role of the server is changed at negotiation and continuity
phases, in which server MUST send packets to measure jitter, latency
and bandwidth. Therefore, the different behaviors of server are
(follow the letter bullets in the figure below):
R) When the client sends messages over TCP (methods BEGIN, READY
Q4S-ALERT, Q4S-RECOVERY and CANCEL) it behaves strictly like a
state machine that receives messages and sends responses.
When the client begins to send UDP messages (methods PING and
BWIDTH), a Q4S server is not strictly a state machine that receives
messages and sends responses because:
S) At latency, jitter and packet loss measurement, the PING
requests are sent periodically by the client but also by the
server. In this case the server behaves as a server answering
client requests but also behaves temporarily as a client, sending
PING requests toward the client and receiving responses.
T) At bandwidth and packet loss measurement, the server sends
BWIDTH requests to the client. In addition, it MUST receive and
process client messages in order to achieve the uplink
measurement.
Garcia Aranda Expires January 18, 2018 [Page 70]
Internet-Draft The Quality for Services Protocol July 2017
The Q4S-ALERT and CANCEL may have a conventional answer if an error
is produced, otherwise the corresponding answer is formatted as a
request message.
.
+-----------+------------------------+-----------+-----------+
| Handshake | Negotiation |Continuity |Termination|
| Phase | Phase | Phase | Phase |
| | | | |
| R ---------> S --> R --> T --> R ---> S --> R ---> R |
| | A | A | | A | | |
| | | | | | | | | | |
| | +-----+ +-----+ | +-----+ | |
| | | | |
+------------------------------------------------+-----------+
Figure 17 Phases & server behaviours.
9. Implementation Recommendations
9.1. Default client constraints
To provide a default configuration, it would be good that the client
had a configurable set of Quality headers in the implementation
settings menu. Otherwise these quality headers will not be present
in the first message.
Different business models (out of scope of this proposal) may be
achieved: depending on who pays for the quality session, the server
can accept certain Client parameters sent in the first message, or
force billing parameters on the server side.
9.2. Latency and Jitter measurements
In execution systems, where the timers are not accurate, a
recommended approach consists of including the optional header
"Timestamp" in the PING request with the time in which the message
has been sent. This allows an accurate measurement of the jitter
even with no identical intervals of time between PINGs.
Garcia Aranda Expires January 18, 2018 [Page 71]
Internet-Draft The Quality for Services Protocol July 2017
9.3. Bandwidth measurements
In programming languages or Operating Systems with timers or limited
clock resolution, it is recommended to use an approach based on
several intervals to send messages of 1KB, in order to reach the
required bandwidth consumption using a rate as close as possible to
a constant rate.
For example, if the resolution is 1 millisecond, and the bandwidth
to reach is 11Mbps, a good approach consists of sending:
1 message of 1KB every 1 millisecond +
1 message of 1KB every 3 milliseconds +
1 message of 1KB every 23 milliseconds
The number of intervals depends on required bandwidth and accuracy
that the programmer wants to achieve.
In execution systems where the timers are not accurate, a
recommended approach consists of checking at each interval, the
number of packets that should have been sent at this timestamp since
origin and send the needed number of packets in order to reach the
required bandwidth.
The shorter packets are used, the more constant is the rate of
bandwidth measurement. However, this may stress the execution system
in charge of receiving and processing packets. As a consequence,
some packets may be lost because of stack overflows. To deal with
this potential issue, a larger packet is recommended (2KB or more)
taking into account the overhead produced by the chunks headers.
9.4. Packet loss measurement resolution
Depending on application nature and network conditions, a packet
loss resolution less than 1% may be needed. In such case, there is
no limit to the number of samples used for this calculation. A
tradeoff between time and resolution should be reached in each case.
For example, in order to have a resolution of 1/10000, the last
10000 samples should be considered in the packetloss measured value.
The problem of this approach is the reliability of old samples. If
the interval used between PING messages is 50ms, then to have a
resolution of 1/1000 it takes 50 seconds and a resolution of 1/10000
Garcia Aranda Expires January 18, 2018 [Page 72]
Internet-Draft The Quality for Services Protocol July 2017
takes 500 seconds (more than 8 minutes). The reliability of a packet
loss calculation based on a sliding window of 8 minutes depends on
how fast network conditions evolve.
9.5. Measurements and reactions
Q4S can be used as a mechanism for measure and trigger network
tuning and application level actions (i.e. lowering video bit-rate,
reduce multiplayer interaction speed, etc) in real-time in order to
reach the application constraints, addressing measured possible
network degradation.
9.6. Instability treatments
There are two scenarios in which Q4S can be affected by network
problems: loss of Q4S packets and outlier samples
9.5.1. Loss of control packets
Lost UDP packets (PING or BWIDTH messages) don't cause any problems
for the Q4S state machine, but if TCP packets are lost, some
undesirable consequences could arise.
Q4S does have protection mechanisms to overcome these situations.
Examples:
o If a BEGIN packet is lost or its corresponding answer, after a
certain timeout, the client SHOULD resend another BEGIN packet,
resetting the session
o If a READY packet is lost, after a certain timeout, the client
SHOULD resend another READY packet.
o If a QOS ALERT request is lost or its corresponding answer,
after a certain timeout, the originator SHOULD resend another
Q4S-ALERT packet.
o If CANCEL request is lost or its corresponding answer, after a
certain timeout, the originator SHOULD resend another CANCEL
packet.
Garcia Aranda Expires January 18, 2018 [Page 73]
Internet-Draft The Quality for Services Protocol July 2017
9.5.2. Outlier samples
Outlier samples are those jitter or latency values far from the
general/average values of most samples.
Hence Q4S default measurement method uses the statistical median
formula for latency calculation, the outlier samples are
neutralized. This is a very common filtering for noise or errors on
signal and image processing.
9.7. Scenarios
Q4S could be used in two scenarios:
o client to ACP (Application content provider)
o client to client (peer to peer scenario)
9.7.1. Client to ACP
One server:
It is the common scenario in which client contact server to
establish a Q4S session.
N servers:
In Content Delivery Networks and in general applications where
delivery of contents can be achieved by different delivery nodes,
two working mechanisms can be defined
o Starting mode: End-user may run Q4S against several delivery
nodes and after some seconds choose the best one to start the
multimedia session
o Prevention mode:During streaming session, user keeps several
Q4S dialogs against different alternative delivery nodes. In
case of congestion, end-user may change to the best alternative
delivery node
Garcia Aranda Expires January 18, 2018 [Page 74]
Internet-Draft The Quality for Services Protocol July 2017
9.7.2. Client to client
In order to solve the client to client scenario, a Q4S register
function MUST be implemented. This allows clients contact each other
for sending the BEGIN message. In this scenario, the Register server
would be used by peers to publish their Q4S-Resource-Server header
and their public IP address to make possible the assumption of
server role.
The register function is out of scope of this protocol version,
because different HTTP mechanisms can be used and Q4S MUST NOT force
any.
10. Security Considerations
Different types of attacks can be avoided. For example, Spoofing of
server IP address can be avoided using the digital signature
mechanism. The network can easily validate this digital signature
using the public key of the server certificate.
This protocol could be supported over IPSec to increase privacy,
although it is out of scope of this proposal.
11. IANA Considerations
A specific port for Q4S TCP control flow mechanism could be
assigned. It could simplify the network implementation. Other
possibility is to use any other port (like 80, HTTP). In this case
the network could use the protocol designator "Q4S" as the mark for
distinguish and treat the packets.
Q4S uses SDP as a container for session information, in which
quality attributes have been added as extended "session-level"
attributes. These set of new attributes should be registered (in
order to avoid the prefix "X-"). In this document, this set of
attributes has been presented as registered attributes.
This is the list of attribute field names to register:
Garcia Aranda Expires January 18, 2018 [Page 75]
Internet-Draft The Quality for Services Protocol July 2017
Attribute name: qos-level
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: defines the current QoS profile in uplink
and downlink for the communication between client and server. The
exact meaning of each level is implementation dependant but in
general, a higher qos-level value corresponds to a better quality
network profile.
Appropriate attribute values: [0..9] "/" [0..9]
Attribute name: alerting-mode
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: defines the receiver of the Q4S alerts sent
by the server. In Q4S-aware-network alerting mode, Q4S alerts are
sent to the client. In this case the network is supposed to be Q4S
aware, and reacts by itself to these alerts. In Reactive alerting
mode, Q4S alerts sent to the network policy server. In this case the
network is not Q4S aware and a specific node (policy server) is
supposed to be in charge of achieving network tuning mechanisms. The
"alerting-mode" attribute is optional, and its default value, when
it is not present, is "Reactive".
Appropriate attribute values:
Attribute name: alert-pause
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: interval of time in milliseconds that the
server must wait between Q4S-ALERT messages in order to allow
network tuning operations. Measurements are not affected by this
pause.
Appropriate attribute values: [0..60000]
Attribute name: public-address
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: contains the public IP address of the client
or the server.
Appropriate attribute values:
Attribute name: latency
Type of attribute: session level
Subject to the charset attribute: NO
Garcia Aranda Expires January 18, 2018 [Page 76]
Internet-Draft The Quality for Services Protocol July 2017
Explanation of purpose: defines the latency constraints in
milliseconds for the communication between client and server.
Appropriate attribute values: [0..9999]
Attribute name: jitter
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: defines the jitter constraints in
milliseconds in uplink and downlink for the communication between
client and server.
Appropriate attribute values: [0..9999] "/" [0..9999]
Attribute name: bandwidth
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: define the bandwidth constraints in kbps in
uplink and downlink for the communication between client and server.
Appropriate attribute values: [0..99999] "/" [0..99999]
Attribute name: packetloss
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: define the packet loss tolerance constraints
in 100% in uplink and downlink for the communication between client
and server.
Appropriate attribute values: [0.00 ..100.00] "/"[0.00 ..100.00]
Attribute name: application
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: define the quality parameter tolerance
constraints with uplink and downlink values for the communication
between the client and the server for four different parameters:
latency, jitter, bandwidth and packetloss.
Attribute values:
[0..9999]
[0..99999] "/" [0..99999]]
Internet-Draft The Quality for Services Protocol July 2017
The "clientListeningPort" is a port in which the client listens for
server requests and MUST be used as origin port of client responses.
The "serverListeningPort" is a port in which server is listening for
incoming messages from the client. The origin port of server
responses may be different than "serverListeningPort" value.
Attribute values:
<0..65535>[ "-" [0..65535]]
Attribute name: measurement
Type of attribute: session level
Subject to the charset attribute: NO
Explanation of purpose: define the procedure to measure the quality
and the different values for each measurement
Attribute values: "procedure/" |
"latency "[0..9999] "/" [0..9999] |
"jitter "[0..9999] "/" [0..9999] |
"bandwidth "[0..99999] "/" [0..99999] |
"packetloss "[0.00..100.00] "/" [0.00..100.00]
If the attribute value is "procedure", the rest of the line MUST
contain the name of the procedure and optional parameters, separated
by ",".
In the case of procedure "default", the valid values are:
a=measurement:procedure default,[0..999]"/" [0..999] "," [0..999]
"/" [0..999] "," [0..9999] "," [0..999]/[0..999] ","
[0..999]/[0..999]
where:
o The first parameter is the interval of time (in milliseconds)
between PING requests during the negotiation phase. Uplink and
downlink values from the client's point of view are separated
by "/". This allows having different responsiveness values
depending on the control resources used in each direction.
o The second parameter is the time interval (in milliseconds)
between PING requests during the continuity phase. Uplink and
downlink values are separated by "/". This allows having two
different responsiveness values depending on the control
resources used in each direction.
o The third parameter is the time interval to be used to measure
bandwidth during the negotiation phase.
Garcia Aranda Expires January 18, 2018 [Page 78]
Internet-Draft The Quality for Services Protocol July 2017
o The fourth parameter indicates the window size for jitter and
latency calculations. Forward and reverse values are separated
by "/".
o The fifth parameter indicates the window size for packet loss
calculations. Forward and reverse values are separated by "/".
Other procedure names are allowed, but at least "default" procedure
implementation is mandatory in client and servers.
12. Conclusions
Q4S defines four phases with different purposes, and inside these
phases the negotiated measurement procedure is used. Basically, Q4S
only defines how to transport SLA information and measurement
results as well as providing some mechanisms for alerting network
and/or application.
Q4S does not ask for resources neither define actions to do in case
quality is degraded. Q4S only alerts if one (or some) of SLA quality
parameters are being violated. Depends on server (Application
content provider) to do something with this information and return
it back to a SLA-compliant state.
Garcia Aranda Expires January 18, 2018 [Page 79]
Internet-Draft The Quality for Services Protocol July 2017
13. References
13.1. Normative References
[1] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,Masinter, L.,
Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --
HTTP/1.1" RFC 2616, June 1999.
[2] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 4566, July 2006.
[3] Bradner, S., "Key words for use in RFCs to Indicate
RequirementLevels", BCP 14, RFC 2119, March 1997.
[4] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 3986, January
2005.
[5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
SDP", RFC 3264, June 2002.
[6] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
April 1992.
[7] Johnsson, J., B. Kaliski, "Public-Key Cryptography Standards
(PCS) #1: RSA Cryptography Specifications version 2.1", RFC
3447, February 2003.
[8] Postel, J., "DoD Standard Transmission Control Protocol", RFC
761, January 1980.
[9] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
1980.
[10] Schulzrinne, H., Casner, S., Frederick, R., Jacobson, V. "RTP:
A Transport Protocol for Real-Time Applications", RFC 3550,
july 2003.
[11] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
RFC 3629, November 2003.
[12] Resnick, P., "Internet Message Format", RFC 5322, October 2008
Garcia Aranda Expires January 18, 2018 [Page 80]
Internet-Draft The Quality for Services Protocol July 2017
13.2. Informative References
[13] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.
Peterson, J., Sparks, R., Handley, M. and Schooler, E. , "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[14] Mathis, M., Semke, J., Mahdavi, J., Ott, T., "The Macroscopic
Behavior of the TCP Congestion Avoidance Algorithm", Computer
Communications Review, 27(3), July 1997.
[15] Floyd, S., "HighSpeed TCP for a Large Congestion Windows", RFC
3649, December 2003.
[16] Rhee, I., Xu, L., Ha, S., "CUBIC for Fast Long-Distance
Networks", Internet-draft draft-rhee-tcpm-cubic-02, February
2009.
[17] Sridharan, M., Tan, K., Bansal, D., Thaler, D., "Compound TCP:
A New TCP Congestion Control for High-Speed and Long Distance
Networks", Internet-draft draft-sridharan-tcpm-ctcp-02,
November, 2008.
Garcia Aranda Expires January 18, 2018 [Page 81]
Internet-Draft The Quality for Services Protocol July 2017
14. Acknowledgments
Many people have made comments and suggestions contributing to this
document. In particular, we would like to thank:
Sonia Herranz Pablo, Clara Cubillo Pastor, Francisco Duran Pina,
Michael Scharf, Jesus Soto Viso and Federico Guillen.
Garcia Aranda Expires January 18, 2018 [Page 82]
Internet-Draft The Quality for Services Protocol July 2017
15. Authors' Addresses
Jose Javier Garcia Aranda
Alcatel-Lucent
C/Maria Tubau 9
28050 Madrid
Spain
Phone: +34 91 330 4348
Email: jose_javier.garcia_granda@nokia.com
Jacobo Perez Lajo
Alcatel-Lucent
C/Maria Tubau 9
28050 Madrid
Spain
Phone: +34 91 330 4165
Email: jacobo.perez@nokia.com
Luis Miguel Diaz Vizcaino
Alcatel-Lucent
C/Maria Tubau 9
28050 Madrid
Spain
Phone: +34 91 330 4871
Email: Luismi.Diaz@nokia.com
Gonzalo Munoz Fernandez
Alcatel-Lucent
C/Maria Tubau 9
28050 Madrid
Spain
Phone: +34 91 330 4000
Email: gonzalo.munoz_fernandez.ext@nokia.com
Carlos Barcenilla
Universidad Politecnica de Madrid
Avenida Complutense 30
28040 Madrid
Spain
Phone: +34 91 549 5700 - 3032
Email: barcenilla@dit.upm.es
Monica Cortes
Universidad Politecnica de Madrid
Avenida Complutense 30
28040 Madrid
Spain
Garcia Aranda Expires January 18, 2018 [Page 83]
Internet-Draft The Quality for Services Protocol July 2017
Phone: +34 91 336 5700 - 3044
Email: cortesm@dit.upm.es
Joaquin Salvachua
Universidad Politecnica de Madrid
Avenida Complutense 30
28040 Madrid
Spain
Phone: +34 91 549 5700 - 3056
Email: jsr@dit.upm.es
Juan Quemada
Universidad Politecnica de Madrid
Avenida Complutense 30
28040 Madrid
Spain
Phone: +34 91 336 7331
Email: jquemada@dit.upm.es
Maribel Narganes
Tecnalia Research & Innovation
Parque Cientifico y Tecnologico de Bizkaia,
Geldo Auzoa, 700 Edificio
48160 Derio, Vizcaya
Spain
Phone: +34 91 336 7331
Email: maribel.narganes@tecnalia.com
Inaki Martinez Sarriegui
Optiva Media
Edificio Europa II,
Calle Musgo 2, 1G,
28023 Madrid
Spain
Phone: +34 91 297 7271
Email: inaki.martinez@optivamedia.com
Lara Fajardo Ibanez
Optiva Media
Edificio Europa II,
Calle Musgo 2, 1G,
28023 Madrid
Spain
Phone: +34 91 297 7271
Email: lara.fajardo@optivamedia.com
Pablo Lopez Zapico
Garcia Aranda Expires January 18, 2018 [Page 84]
Internet-Draft The Quality for Services Protocol July 2017
Optiva Media
Edificio Europa II,
Calle Musgo 2, 1G,
28023 Madrid
Spain
Phone: +34 91 297 7271
Email: Pablo.lopez@optivamedia.com
Garcia Aranda Expires January 18, 2018 [Page 85]